scholarly journals Whole-cell clamp of dissociated photoreceptors from the eye of Lima scabra.

1991 ◽  
Vol 97 (1) ◽  
pp. 35-54 ◽  
Author(s):  
E Nasi
Keyword(s):  
Calcium Influx ◽  
Large Fraction ◽  
Outward Current ◽  
Light Response ◽  
Stimulus Onset ◽  
Delayed Rectifier ◽  
Transient Outward Current ◽  
Whole Cell ◽  
Inward Current ◽  
Voltage Dependent

Voltage-dependent membrane currents were investigated in enzymatically dissociated photoreceptors of Lima scabra using the whole-cell clamp technique. Depolarizing steps to voltages more positive than -10 mV elicit a transient inward current followed by a delayed, sustained outward current. The outward current is insensitive to replacement of a large fraction of extracellular Cl- with the impermeant anion glucuronate. Superfusion with tetraethylammonium and 4-aminopyridine reversibly abolishes the outward current, and internal perfusion with cesium also suppresses it, indicating that it is mediated by potassium channels. Isolation of the inward current reveals a fast activation kinetics, the peak amplitude occurring as early as 4-5 ms after stimulus onset, and a relatively rapid, though incomplete inactivation. Within the range of voltages examined, spanning up to +90 mV, reversal was not observed. The inward current is not sensitive to tetrodotoxin at concentrations up to 10 microM, and survives replacement of extracellular Na with tetramethylammonium. On the other hand, it is completely eliminated by calcium removal from the perfusing solution, and it is partially blocked by submillimolar concentrations of cadmium, suggesting that it is entirely due to voltage-dependent calcium channels. Analysis of the kinetics and voltage dependence of the isolated calcium current indicates the presence of two components, possibly reflecting the existence of separate populations of channels. Barium and strontium can pass through these channels, though less easily than calcium. Both the activation and the inactivation become significantly more sluggish when these ions serve as the charge carrier. A large fraction of the outward current is activated by preceding calcium influx. Suppression of this calcium-dependent potassium current shows a small residual component resembling the delayed rectifier. In addition, a transient outward current sensitive to 4-aminopyridine (Ia) could also be identified. The relevance of such conductance mechanisms in the generation of the light response in Lima photoreceptors is discussed.

Transient potassium currents in avian sensory neurons

1990 ◽  
Vol 63 (4) ◽  
pp. 725-737 ◽  
Author(s):  
S. K. Florio ◽  
C. D. Westbrook ◽  
M. R. Vasko ◽  
R. J. Bauer ◽  
J. L. Kenyon
Keyword(s):  
Single Channel ◽  
Outward Current ◽  
Potassium Currents ◽  
Delayed Rectifier ◽  
Transient Outward Current ◽  
Single Channels ◽  
Patch Clamp Technique ◽  
Small Component ◽  
Whole Cell ◽  
Outward Currents

1. We used the patch-clamp technique to study voltage-activated transient potassium currents in freshly dispersed and cultured chick dorsal root ganglion (DRG) cells. Whole-cell and cell-attached patch currents were recorded under conditions appropriate for recording potassium currents. 2. In whole-cell experiments, 100-ms depolarizations from normal resting potentials (-50 to -70 mV) elicited sustained outward currents that inactivated over a time scale of seconds. We attribute this behavior to a component of delayed rectifier current. After conditioning hyperpolarizations to potentials negative to -80 mV, depolarizations elicited transient outward current components that inactivated with time constants in the range of 8-26 ms. We attribute this behavior to a transient outward current component. 3. Conditioning hyperpolarizations increased the rate of activation of the net outward current implying that the removal of inactivation of the transient outward current allows it to contribute to early outward current during depolarizations from negative potentials. 4. Transient current was more prominent on the day the cells were dispersed and decreased with time in culture. 5. In cell-attached patches, single channels mediating outward currents were observed that were inactive at resting potentials but were active transiently during depolarizations to potentials positive to -30 mV. The probability of channels being open increased rapidly (peaking within approximately 6 ms) and then declined with a time constant in the range of 13-30 ms. With sodium as the main extracellular cation, single-channel conductances ranged from 18 to 32 pS. With potassium as the main extracellular cation, the single-channel conductance was approximately 43 pS, and the channel current reversed near 0 mV, as expected for a potassium current. 6. We conclude that the transient potassium channels mediate the component of transient outward current seen in the whole-cell experiments. This current is a relatively small component of the net current during depolarizations from normal resting potentials, but it can contribute significant outward current early in depolarizations from hyperpolarized potentials.

scholarly journals Voltage-dependent conductances in Limulus ventral photoreceptors.

1982 ◽  
Vol 79 (2) ◽  
pp. 187-209 ◽  
Author(s):  
J E Lisman ◽  
G L Fain ◽  
P M O'Day
Keyword(s):  
Outward Current ◽  
Delayed Rectifier ◽  
Molluscan Neurons ◽  
Inward Current ◽  
Transient Component ◽  
Outward Currents ◽  
Voltage Dependent ◽  
Inward Currents ◽  
K Current ◽  
A Current

The voltage-dependent conductances of Limulus ventral photoreceptors have been investigated using a voltage-clamp technique. Depolarization in the dark induces inward and outward currents. The inward current is reduced by removing Na+ or Ca2+ and is abolished by removing both ions. These results suggest that both Na+ and Ca2+ carry voltage-dependent inward current. Inward current is insensitive to tetrodotoxin but is blocked by external Ni2+. The outward current has a large transient component that is followed by a smaller maintained component. Intracellular tetraethylammonium preferentially reduces the maintained component, and extracellular 4-amino pyridine preferentially reduces the transient component. Neither component is strongly affected by removal of extracellular Ca2+ or by intracellular injection of EGTA. It is concluded that the photoreceptors contain at least three separate voltage-dependent conductances: 1) a conductance giving rise to inward currents; 2) a delayed rectifier giving rise to maintained outward K+ current; and 3) a rapidly inactivating K+ conductance similar to the A current of molluscan neurons.

A maturational shift in pulmonary K+ channels, from Ca2+ sensitive to voltage dependent

1998 ◽  
Vol 275 (6) ◽  
pp. L1019-L1025 ◽  
Author(s):  
Helen L. Reeve ◽  
E. Kenneth Weir ◽  
Stephen L. Archer ◽  
David N. Cornfield
Keyword(s):  
Pulmonary Circulation ◽  
Acute Hypoxia ◽  
Outward Current ◽  
Resting Membrane Potential ◽  
Transient Outward Current ◽  
Abrupt Decrease ◽  
Whole Cell ◽  
Electrophysiological Properties ◽  
Voltage Dependent ◽  
Intracellular Ca

The mechanism responsible for the abrupt decrease in resistance of the pulmonary circulation at birth may include changes in the activity of O2-sensitive K+ channels. We characterized the electrophysiological properties of fetal and adult ovine pulmonary arterial (PA) smooth muscle cells (SMCs) using conventional and amphotericin B-perforated patch-clamp techniques. Whole cell K+ currents of fetal PASMCs in hypoxia were small and characteristic of spontaneously transient outward currents. The average resting membrane potential (RMP) was −36 ± 3 mV and could be depolarized by charybdotoxin (100 nM) or tetraethylammonium chloride (5 mM; both blockers of Ca2+-dependent K+ channels) but not by 4-aminopyridine (4-AP; 1 mM; blocker of voltage-gated K+ channels) or glibenclamide (10 μM; blocker of ATP-dependent K+channels). In hypoxia, chelation of intracellular Ca2+ by 5 mM 1,2-bis(2-aminophenoxy)ethane- N, N, N′, N′-tetraacetic acid further reduced the amplitude of the whole cell K+ current and prevented spontaneously transient outward current activity. Under these conditions, the remaining current was partially inhibited by 1 mM 4-AP. K+ currents of fetal PASMCs maintained in normoxia were not significantly reduced by acute hypoxia. In normoxic adult PASMCs, whole cell K+ currents were large and RMP was −49 ± 3 mV. These 4-AP-sensitive K+ currents were partially inhibited by exposure to acute hypoxia. We conclude that the K+ channel regulating RMP in the ovine pulmonary circulation changes after birth from a Ca2+-dependent K+ channel to a voltage-dependent K+ channel. The maturational-dependent differences in the mechanism of the response to acute hypoxia may be due to this difference in K+ channels.

Calcium and potassium currents in the fast coxal depressor motor neuron of the cockroach Periplaneta americana

1995 ◽  
Vol 74 (5) ◽  
pp. 2043-2050 ◽  
Author(s):  
J. A. David ◽  
R. M. Pitman
Keyword(s):  
Motor Neuron ◽  
Periplaneta Americana ◽  
Outward Current ◽  
Potassium Currents ◽  
Transient Outward Current ◽  
Potential Range ◽  
Inward Current ◽  
Outward Currents ◽  
Current Voltage ◽  
Voltage Dependent

1. Membrane currents have been examined in the cell body of the fast coxal depressor motor neuron (Df) of the cockroach Periplaneta americana with the use of two-electrode voltage clamp. 2. Most of the outward current induced by membrane depolarizations to between -40 and +80 mV was carried by K+ because it was blocked by external tetraethylammonium+ (TEA+; 20 mM) and internal Cs+. 3. Over the potential range -20 to +80 mV, a large proportion of this TEA+/Cs(+)-sensitive K+ current consisted of two temporal components, a transient outward current (IKtrans) and a sustained outward current (IKsus). IKtrans and a large proportion of IKsus appeared to be calcium-activated potassium currents (IK,Ca,trans and IK,Ca,sus, respectively) because these were suppressed by injecting ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA), removing Ca2+ from the saline or replacing Ca2+ with Ba2+. After suppression of IK,Ca by internal EGTA or Ca(2+)-free saline, membrane depolarizations positive to -40 mV induced voltage-dependent outward currents (IK,V), which consisted of single-component outward relaxations. 4. When outward currents were blocked by external TEA+/internal Cs+, a voltage-dependent inward current consisting of a transient and a sustained component was observed over the potential range -40 to +40 mV. Both components of this inward current appeared to be carried by Ca2+ because they were blocked by external Cd2+ (1 mM), verapamil (0.1 mM), nifedipine (0.1 mM), or diltiazem (0.1 mM). 5. Both the transient component of the calcium current (ICa,trans) and the sustained component (ICa,sus) were maximal at 0 mV and present when Ca2+ in the saline were replaced by Ba2+. The inactivation of ICa,trans is voltage dependent, the rate of inactivation increasing with membrane depolarization. 6. The current-voltage relationships of Ca2+ currents differed from those of calcium-activated K+ currents. It is proposed that the discrepancy between these current-voltage relationships arises from the rapidity with which IK,Ca is saturated by Ca2+ entering through voltage-dependent channels and because the apparent reversal potential for ICa is not at ECa. 7. Although the similarity in the shape of IK,Ca and ICa might suggest that the time course of IK,Ca is determined by the kinetics of ICa, this appears unlikely in view of the rapid saturation of IK,Ca by Ca2+, which considerably outlasts the period of Ca2+ influx.

A- and C-type rat nodose sensory neurons: model interpretations of dynamic discharge characteristics

1994 ◽  
Vol 71 (6) ◽  
pp. 2338-2358 ◽  
Author(s):  
J. H. Schild ◽  
J. W. Clark ◽  
M. Hay ◽  
D. Mendelowitz ◽  
M. C. Andresen ◽  
...  
Keyword(s):  
Action Potential ◽  
Sensory Neurons ◽  
Outward Current ◽  
Delayed Rectifier ◽  
Transient Outward Current ◽  
Current Clamp ◽  
Patch Clamp Technique ◽  
Whole Cell ◽  
Response Properties ◽  
Wide Range

1. Neurons of the nodose ganglia provide the sole connection between many types of visceral sensory inputs and the central nervous system. Electrophysiological studies of isolated nodose neurons provide a practical means of measuring individual cell membrane currents and assessing their putative contributions to the overall response properties of the neuron and its terminations. Here, we present a comprehensive mathematical model of an isolated nodose sensory neuron that is based upon numerical fits to quantitative voltage- and current-clamp data recorded in our laboratory. Model development was accomplished using an iterative process of electrophysiological recordings, nonlinear parameter estimation, and computer simulation. This work is part of an integrative effort aimed at identifying and characterizing the fundamental ionic mechanisms participating in the afferent neuronal limb of the baroreceptor reflex. 2. The neuronal model consists of two parts: a Hodgkin-Huxley-type membrane model coupled to a lumped fluid compartment model that describes Ca2+ ion concentration dynamics within the intracellular and external perineuronal media. Calcium buffering via a calmodulin-type buffer is provided within the intracellular compartment. 3. The complete model accurately reproduces whole-cell voltage-clamp recordings of the major ion channel currents observed in enzymatically dispersed nodose sensory neurons. Specifically, two Na+ currents exhibiting fast (INaf) and slow tetrodotoxin (TTX)-insensitive (INas) kinetics; low- and high-threshold Ca2+ currents exhibiting transient (ICa,t) and long-lasting (ICa,n) dynamics, respectively; and outward K+ currents consisting of a delayed-rectifier current (IK), a transient outward current (I(t)) and a Ca(2+)-activated K+ current (IK,Ca). 4. Whole-cell current-clamp recordings of somatic action-potential dynamics were performed on enzymatically dispersed nodose neurons using the perforated patch-clamp technique. Stimulus protocols consisted of both short (< or = 2.0 ms) and long (> or = 200 ms) duration current pulses over a wide range of membrane holding potentials. These studies clearly revealed two populations of nodose neurons, often termed A- and C-type cells, which exhibit markedly different action-potential signatures and stimulus response properties. 5. Using a single set of equations, the model accurately reproduces the electrical behavior of both A- and C-type nodose neurons in response to a wide variety of stimulus conditions and membrane holding potentials. The structure of the model, as well as the majority of its parameters are the same for both A- and C-type implementations.(ABSTRACT TRUNCATED AT 400 WORDS)

Whole-cell recording of light-evoked photoreceptor responses in a slice preparation of the cuttlefish retina

2005 ◽  
Vol 22 (3) ◽  
pp. 359-370 ◽  
Author(s):  
ABDESSLAM CHRACHRI ◽  
LISA NELSON ◽  
RODDY WILLIAMSON
Keyword(s):  
Time Course ◽  
Early Stage ◽  
Outward Current ◽  
Delayed Rectifier ◽  
Dependent Manner ◽  
Slice Preparation ◽  
Whole Cell ◽  
Inward Current ◽  
Transient Inward Current ◽  
Dose Dependent

A new tissue slice preparation of the cuttlefish eye is described that permits patch-clamp recordings to be acquired from intact photoreceptors during stimulation of the retina with controlled light flashes. Whole-cell recordings using this preparation, from the retinas of very youngSepia officinalisdemonstrated that the magnitude, latency, and kinetics of the flash-induced photocurrent are closely dependent on the magnitude of the flash intensity. Depolarizing steps to voltages more positive than −40 mV, from a membrane holding potential of −60 mV, induced a transient inward current followed by a larger, more sustained outward current in these early-stage photoreceptors. The latter current resembled the delayed rectifier (IK) already identified in many other nerve cells, including photoreceptors. This current was activated at −30 mV from a holding potential of −60 mV, had a sustained time course, and was blocked in a dose-dependent manner by tetraethylammonium chloride (TEA). The smaller, transient, inward current appeared at potentials more positive than −50 mV, reached peak amplitude at −30 mV and decreased with further depolarization. This current was characterized as the sodium current (INa) on the basis that it was inactivated at holding potentials above −40 mV, was blocked by tetrodotoxin (TTX) and was insensitive to cobalt.Intracellular perfusion of the photoreceptors,viathe patch pipette, demonstrated that U-73122 and heparin blocked the evoked photocurrent in a dose-dependent manner, suggesting the involvement of the phospholipase C (PLC) and inositol 1,4,5-triphosphate (InsP3), respectively, in the phototransduction cascade. Perfusion with cyclic GMP increased significantly the evoked photocurrent, while the inclusion of phorbol-12,13-dibutyrate reduced significantly the evoked photocurrent, supporting the involvement of cGMP and the diacylglycerol (DAG) pathways, respectively, in the cuttlefish transduction process.

Rat hippocampal neurons in culture: potassium conductances

1984 ◽  
Vol 51 (6) ◽  
pp. 1409-1433 ◽  
Author(s):  
M. Segal ◽  
J. L. Barker
Keyword(s):  
Time Constant ◽  
Hippocampal Neurons ◽  
Outward Current ◽  
Resting Potential ◽  
Equilibrium Potential ◽  
Transient Outward Current ◽  
Current Response ◽  
Normal Medium ◽  
Inward Current ◽  
Voltage Dependent

Two-electrode voltage-clamp methodology was used to analyze voltage-dependent ionic conductances in 81 rat hippocampal neurons grown in culture for 4-6 wk. Pyramidal and multipolar cells with 15- to 20-micron-diameter cell bodies were impaled with two independent KCl electrodes. The cells had resting potentials of -30 to -60 mV and an average input resistance of about 30 M omega. A depolarizing command applied to a cell maintained in normal medium invariably evoked a fast (2-10 ms) inward current that saturated the current-passing capacity of the system. This was blocked in a reversible manner by application of tetrodotoxin (TTX) (0.1-1.0 microM) near the recorded cell. In the presence of TTX, a depolarizing command evoked a rapidly rising (3-5 ms), rapidly decaying (25 ms) transient outward current reminiscent of "IA" reported in molluscan neurons. This was followed by a more slowly activating (approximately 100 ms) outward current response of greater amplitude that decayed with a time constant of about 2-3 s. These properties resemble those associated with the K+ conductance, IK, underlying delayed rectification described in many excitable membranes. IK was blocked by extracellular application of tetraethylammonium (TEA) but was insensitive to 4-aminopyridine (4-AP) at concentrations that effectively eliminated IA. IA, in turn, was only marginally depressed by TEA. Unlike IK, IA was completely inactivated when the membrane was held at potentials positive to -50 mV. Inactivation was completely removed by conditioning hyperpolarization at -90 mV. A brief hyperpolarizing pulse (10 ms) was sufficient to remove 95% of the inactivation. IA activated on commands to potentials more positive than -50 mV. The inversion potential of the ionic conductance underlying IA and IK was in the range of the K+ equilibrium potential, EK, as measured by the inversion of tail currents; and this potential was shifted in a depolarizing direction by elevated [K+]0. Thus, both current species reflect activation of membrane conductance to K+ ions. Hyperpolarizing commands from resting potentials revealed a time- and voltage-dependent slowly developing inward current in the majority of cells studied. This membrane current was observed in cells exhibiting "anomalous rectification" and was therefore labeled IAR. It was activated at potentials negative to -70 mV with a time constant of 100-200 ms and was not inactivated. A return to resting potential revealed a tail current that disappeared at about EK. IAR was blocked by extracellular CS+ and was enhanced by elevating [K+]0. It thus appears to be carried by inward movement of K+ ions.(ABSTRACT TRUNCATED AT 400 WORDS)

Layer I neurons of the rat neocortex. II. Voltage-dependent outward currents

1996 ◽  
Vol 76 (2) ◽  
pp. 668-682 ◽  
Author(s):  
F. M. Zhou ◽  
J. J. Hablitz
Keyword(s):  
Time Constant ◽  
Time Course ◽  
Outward Current ◽  
Pyramidal Cells ◽  
Delayed Rectifier ◽  
Transient Outward Current ◽  
Pharmacological Properties ◽  
Voltage Dependent ◽  
Steady State Inactivation ◽  
Layer I

1. Whole cell patch-clamp techniques, combined with direct visualization of neurons, were used to study voltage-dependent potassium currents in layer 1 neurons and layer II/III pyramidal cells. 2. In the presence of tetrodotoxin, step depolarizations evoked an outward current. This current had a complex waveform and appeared to be a composite of early and late components. The early peak of the composite K+ outward current was larger in layer I neurons. 3. In both layer I and pyramidal cells, the composite outward K+ current could be separated into two components based on kinetic and pharmacological properties. The early component was termed I(A) because it was a transient outward current activating rapidly and then decaying. I(A) was more sensitive to blocking by 4-aminopyridine (4-AP) than tetraethylammonium (TEA). The second component, termed the delayed rectifier or I(DR), activated relatively slowly and did not decay significantly during a 200-ms test pulse. I(DR) was insensitive to blocking by 4-AP at concentrations up to 4 mM and blocked by > 60% by 40-60 mM TEA. 4. I(A) kinetics were examined in the presence of 40-60 mM TEA. Under these conditions, I(A) began to activate between -40 and -30 mV. Half-maximal activation occurred around 0 mV. In both layer I and pyramidal cells, the half-inactivation potential (Vh-inact) was around or more positive than -50 mV. At -60 mV, > 70% of I(A) conductance was available. I(A) decayed along a single exponential time course with a time constant of approximately 15 ms. This decay showed little voltage dependence. 5. In both layer I and pyramidal cells, I(DR) was studied in the presence of 4 mM 4-AP to block I(A) and in saline containing 0.2 mM Ca2+ and 3.6 mM Mg2+ to reduce contributions from Ca2+-dependent K+ currents. Under these conditions, I(DR) began to activate at -35 to -25 mV with Vh-act of 3.6 +/- 4.5 mV (mean +/- SD). The 10-90% rise time of I(DR) was 15 ms at 30 mV. At 2.2 ms after the onset of the command potential to +30 mV, I(DR) could reach a significant amplitude (approximately 1.5 nA in layer I neurons and 2.2 nA in pyramidal cells depending on the cell size). When long test pulses (> or = 1,000 ms) were used, a decay time constant approximately 800 ms at +40 mV was observed. In both layer I and pyramidal cells, steady state inactivation of I(DR) was minimal. 6. These results indicate that I(A) and I(DR) are the two major hyperpolarizing currents in layer I and pyramidal cells. The kinetics and pharmacological properties of I(A) and I(DR) were not significantly different in fast-spiking layer I neurons and regular-spiking layer II/III pyramidal cells. The relatively positive activation threshold (more than or equal to -40 mV) of both I(A) and I(DR) suggest that they do not play a role in neuronal behavior below action potential (AP) threshold and that their properties are more suitable to repolarize AP. The greater density of I(A) in layer I neurons appears responsible for fast spike generation.

scholarly journals Potassium Currents in Freshly Dissociated Uterine Myocytes from Nonpregnant and Late-Pregnant Rats

1998 ◽  
Vol 112 (6) ◽  
pp. 737-756 ◽  
Author(s):  
S.Y. Wang ◽  
M. Yoshino ◽  
J.L. Sui ◽  
M. Wakui ◽  
P.N. Kao ◽  
...  
Keyword(s):  
Outward Current ◽  
Late Pregnancy ◽  
Delayed Rectifier ◽  
Transient Outward Current ◽  
Taenia Coli ◽  
Open Probability ◽  
Pregnant Rats ◽  
Whole Cell ◽  
Small Conductance ◽  
K Currents

In freshly dissociated uterine myocytes, the outward current is carried by K+ through channels highly selective for K+. Typically, nonpregnant myocytes have rather noisy K+ currents; half of them also have a fast-inactivating transient outward current (ITO). In contrast, the current records are not noisy in late pregnant myocytes, and ITO densities are low. The whole-cell IK of nonpregnant myocytes respond strongly to changes in [Ca2+]o or changes in [Ca2+]i caused by photolysis of caged Ca2+ compounds, nitr 5 or DM-nitrophene, but that of late-pregnant myocytes respond weakly or not at all. The Ca2+ insensitivity of the latter is present before any exposure to dissociating enzymes. By holding at −80, −40, or 0 mV and digital subtractions, the whole-cell IK of each type of myocyte can be separated into one noninactivating and two inactivating components with half-inactivation at approximately −61 and −22 mV. The noninactivating components, which consist mainly of iberiotoxin-susceptible large-conductance Ca2+-activated K+ currents, are half-activated at 39 mV in nonpregnant myocytes, but at 63 mV in late-pregnant myocytes. In detached membrane patches from the latter, identified 139 pS, Ca2+-sensitive K+ channels also have a half-open probability at 68 mV, and are less sensitive to Ca2+ than similar channels in taenia coli myocytes. Ca2+-activated K+ currents, susceptible to tetraethylammonium, charybdotoxin, and iberiotoxin contribute 30–35% of the total IK in nonpregnant myocytes, but &lt;20% in late-pregnant myocytes. Dendrotoxin-susceptible, small-conductance delayed rectifier currents are not seen in nonpregnant myocytes, but contribute ∼20% of total IK in late-pregnant myocytes. Thus, in late-pregnancy, myometrial excitability is increased by changes in K+ currents that include a suppression of the ITO, a redistribution of IK expression from large-conductance Ca2+-activated channels to smaller-conductance delayed rectifier channels, a lowered Ca2+ sensitivity, and a positive shift of the activation of some large-conductance Ca2+-activated channels.

The actions of hydrogen sulfide on dorsal raphe serotonergic neurons in vitro

1993 ◽  
Vol 70 (1) ◽  
pp. 81-96 ◽  
Author(s):  
S. B. Kombian ◽  
R. J. Reiffenstein ◽  
W. F. Colmers
Keyword(s):  
Hydrogen Sulfide ◽  
Outward Current ◽  
Rapid Onset ◽  
Dorsal Raphe ◽  
Membrane Properties ◽  
Delayed Rectifier ◽  
Inward Current ◽  
Voltage Dependent ◽  
Dorsal Raphé

1. The actions of hydrogen sulfide (HS-) on membrane and synaptic properties of dorsal raphe (DR) serotonergic cells were studied in the in vitro brain stem slice preparation, using intracellular sharp microelectrode and whole-cell recording techniques. 2. Sulfide produced two reversible, concentration-dependent effects on resting membrane properties of DR cells: (1) 14% responded to HS- with a slow onset hyperpolarization or an outward current accompanied by an conductance increase in voltage clamp (holding potential = -60 mV; monophasic outward cell) or (2) 39% responded with a rapid-onset depolarization corresponding to a weakly voltage-dependent inward current showing little or no change in conductance between -115 and -40 mV (monophasic inward cell). In addition, 29.5% showed both the above effects, responding first with a rapid-onset depolarization and then a sustained hyperpolarization. Such cells had membrane currents very similar to those seen in the monophasic inward and outward cells (biphasic cells). Finally, 17.5% of DR cells had no measurable postsynaptic membrane response to HS-. 3. The outward current induced in the presence of HS- had a reversal potential of about -90 mV when recorded either with 2 M KCl or 145 mM potassium gluconate in the pipette and was accompanied by an increase in conductance, suggesting that it is caused by an elevated conductance to K+. 4. This current was sensitive to the removal of external Ca2+ and blockade by Cd2+, suggesting that it is activated by an elevation in internal [Ca2+]. It was also blocked by apamin or Ba2+ and Cs+, both of which revealed an underlying inward current. The outward current was insensitive to the application of a large variety of antagonists to other known voltage- and calcium-dependent K+ channels. Elevation of intracellular ATP using a patch pipette did not prevent the activation of the outward current. 5. HS- reversibly suppressed a voltage-dependent outward current activated in the voltage range of -50 to -40 mV. This current was also blocked by 10 mM tetraethylammonium, suggesting that HS- suppresses the delayed rectifier in DR cells. 6. The inward current could be observed in the presence of HS- not only in monophasic inward cells but also in monophasic outward or biphasic cells whose outward current was selectively blocked. This inward current was sensitive to the removal of extracellular Ca2+, or the the application of relatively low concentrations of Cd2+, suggesting that it is carried by Ca2+. Both these manipulations also blocked the outward current in monophasic outward or biphasic cells.(ABSTRACT TRUNCATED AT 400 WORDS)

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