scholarly journals Voltage-gated transient currents in bovine adrenal fasciculata cells. II. A-type K+ current.

1993 ◽  
Vol 102 (2) ◽  
pp. 239-255 ◽  
Author(s):  
B Mlinar ◽  
J J Enyeart
Keyword(s):  
Hormone Secretion ◽  
Inactivation Kinetics ◽  
Zona Fasciculata ◽  
Time Constants ◽  
Whole Cell ◽  
Type K ◽  
Slow Kinetics ◽  
Boltzmann Function ◽  
Voltage Dependent ◽  
K Current

In whole cell patch clamp recordings on enzymatically dissociated adrenal zona fasciculata (AZF) cells, a rapidly inactivating A-type K+ current was observed in each of more than 150 cells. Activation of IA was steeply voltage dependent and could be described by a Boltzmann function raised to an integer power of 4, with a midpoint of -28.3 mV. Using the "limiting logarithmic potential sensitivity," the single channel gating charge was estimated to be 7.2 e. Voltage-dependent inactivation could also be described by a Boltzmann function with a midpoint of -58.7 mV and a slope factor of 5.92 mV. Gating kinetics of IA included both voltage-dependent and -independent transitions in pathways between closed, open, and inactivated states. IA activated with voltage-dependent sigmoidal kinetics that could be fit with an n4h formalism. The activation time constant, tau a, reached a voltage-independent minimum at potentials positive to 0 mV. IA currents inactivated with two time constants that were voltage independent at potentials ranging from -30 to +45 mV. At +20 mV, tau i(fast) and tau i(slow) were 13.16 +/- 0.64 and 62.26 +/- 5.35 ms (n = 34), respectively. In some cells, IA inactivation kinetics slowed dramatically after many minutes of whole cell recording. Once activated by depolarization, IA channels returned to the closed state along pathways with two voltage-dependent time constants which were 0.208 s, tau rec-f and 10.02 s, tau rec-s at -80 mV. Approximately 90% of IA current recovered with slow kinetics at potentials between -60 and -100 mV. IA was blocked by 4-aminopyridine (IC50 = 629 microM) through a mechanism that was strongly promoted by channel activation. Divalent and trivalent cations including Ni2+ and La3+ also blocked IA with IC50's of 467 and 26.4 microM, respectively. With respect to biophysical properties and pharmacology, IA in AZF cells resembles to some extent transient K+ currents in neurons and muscle, where they function to regulate action potential frequency and duration. The function of this prominent current in steroid hormone secretion by endocrine cells that may not generate action potentials is not yet clear.

Isolation and characterization of a persistent potassium current in neostriatal neurons

1996 ◽  
Vol 76 (2) ◽  
pp. 1180-1194 ◽  
Author(s):  
E. S. Nisenbaum ◽  
C. J. Wilson ◽  
R. C. Foehring ◽  
D. J. Surmeier
Keyword(s):  
Voltage Dependence ◽  
Membrane Potentials ◽  
Time Constants ◽  
Whole Cell ◽  
Boltzmann Function ◽  
Voltage Dependent ◽  
Slope Factor ◽  
K Current ◽  
Kinetics Of ◽  
K Currents

1. Depolarization-activated, calcium-independent potassium (K+) currents were studied with the use of whole cell voltage-clamp recording from neostriatal neurons acutely isolated from adult (> or = 4 wk old) rats. The whole cell K+ current was composed of transient and persistent components. The aims of the experiments were to isolate the persistent component and then to characterize its voltage dependence and kinetics. 2. Application of 10 mM 4-aminopyridine (4-AP) completely blocked the transient currents while reducing the persistent current by approximately 40% [50% inhibitory concentration (IC50), of blockable current = 125 microM]. The persistent K+ current also was reduced by tetraethylammonium (TEA). Two components to the TEA block were present, having IC50s of 125 microM (23% of the blockable current) and 5.9 mM (77% of the blockable current). Collectively, these results suggested that the persistent components of the total K+ current was pharmacologically heterogeneous. The properties of the 4-AP-resistant, persistent K+ current (IKrp) were subsequently studied. 3. The kinetics of activation and deactivation of IKrp were voltage dependent. Examination of the entire activation/deactivation time constant profile showed that it was bell shaped, with time constants being moderately rapid (tau approximately 50 ms) at membrane potentials corresponding to the resting potential of neostriatal cells (approximately -80 mV), becoming considerably longer (tau approximately 100 ms) at potentials near the cells' spike thresholds (approximately -45 mV), and decreasing to a minimum (tau approximately 5 ms) at potentials associated with the peak of the cells' action potentials (approximately +20 mV). The inactivation kinetics of IKrp also were voltage dependent. The time constants of inactivation varied between 1 and 8 s at potentials between -10 and +35 mV. 4. Unlike persistent K+ currents in many other cell types, IKrp activated at relatively hyperpolarized membrane potentials (approximately -70 mV). The Boltzmann function describing activation had a half-activation voltage of -13 mV and a slope factor of 12 mV. In addition, the Boltzmann function describing the voltage dependence of inactivation of IKrp had a relatively depolarized half-inactivation voltage of -55 and a large slope factor of 19 mV, indicating that this current was available over a broad range of membrane potentials (between -100 and -10 mV). 5. Neostriatal neurons recorded in vivo exhibit subthreshold shifts in membrane potential of variable duration (tens of ms to s) from a hyperpolarized resting state to a depolarized state that is limited in amplitude just below spike threshold. The voltage dependence of activation and inactivation of IKrp indicates that it will be available on depolarization from the hyperpolarized state. However, the slow activation rate of this current suggests that it will contribute little either to limiting the amplitude of the initial depolarization associated with entry into the depolarized state or to depolarizing episodes of short duration (e.g., < 50 ms). However, IKrp should limit the amplitude of membrane depolarizations associated with prolonged excursions into the depolarized state.

scholarly journals Voltage-gated transient currents in bovine adrenal fasciculata cells. I. T-type Ca2+ current.

1993 ◽  
Vol 102 (2) ◽  
pp. 217-237 ◽  
Author(s):  
B Mlinar ◽  
B A Biagi ◽  
J J Enyeart
Keyword(s):  
Time Constant ◽  
Low Voltage ◽  
Zona Fasciculata ◽  
Patch Clamp Technique ◽  
Time Constants ◽  
Voltage Gated ◽  
Wide Range ◽  
Boltzmann Function ◽  
Voltage Dependent ◽  
Ca2 Channels

The whole cell version of the patch clamp technique was used to identify and characterize voltage-gated Ca2+ channels in enzymatically dissociated bovine adrenal zona fasciculata (AZF) cells. The great majority of cells (84 of 86) expressed only low voltage-activated, rapidly inactivating Ca2+ current with properties of T-type Ca2+ current described in other cells. Voltage-dependent activation of this current was fit by a Boltzmann function raised to an integer power of 4 with a midpoint at -17 mV. Independent estimates of the single channel gating charge obtained from the activation curve and using the "limiting logarithmic potential sensitivity" were 8.1 and 6.8 elementary charges, respectively. Inactivation was a steep function of voltage with a v1/2 of -49.9 mV and a slope factor K of 3.73 mV. The expression of a single Ca2+ channel subtype by AZF cells allowed the voltage-dependent gating and kinetic properties of T current to be studied over a wide range of potentials. Analysis of the gating kinetics of this Ca2+ current indicate that T channel activation, inactivation, deactivation (closing), and reactivation (recovery from inactivation) each include voltage-independent transitions that become rate limiting at extreme voltages. Ca2+ current activated with voltage-dependent sigmoidal kinetics that were described by an m4 model. The activation time constant varied exponentially at test potentials between -30 and +10 mV, approaching a voltage-independent minimum of 1.6 ms. The inactivation time constant (tau i) also decreased exponentially to a minimum of 18.3 ms at potentials positive to 0 mV. T channel closing (deactivation) was faster at more negative voltages; the deactivation time constant (tau d) decreased from 8.14 +/- 0.7 to 0.48 +/- 0.1 ms at potentials between -40 and -150 mV. T channels inactivated by depolarization returned to the closed state along pathways that included two voltage-dependent time constants. tau rec-s ranged from 8.11 to 4.80 s when the recovery potential was varied from -50 to -90 mV, while tau rec-f decreased from 1.01 to 0.372 s. At potentials negative to -70 mV, both time constants approached minimum values. The low voltage-activated Ca2+ current in AZF cells was blocked by the T channel selective antagonist Ni2+ with an IC50 of 20 microM. At similar concentrations, Ni2+ also blocked cortisol secretion stimulated by adrenocorticotropic hormone. Our results indicate that bovine AZF cells are distinctive among secretory cells in expressing primarily or exclusively T-type Ca2+ channels.(ABSTRACT TRUNCATED AT 400 WORDS)

Extracellular Ba2+ blocks the cardiac transient outward K+ current

2000 ◽  
Vol 278 (1) ◽  
pp. H295-H299 ◽  
Author(s):  
Hong Shi ◽  
Hui-Zhen Wang ◽  
Zhiguo Wang
Keyword(s):  
Patch Clamp ◽  
Inward Rectifier ◽  
Delayed Rectifier ◽  
Inactivation Kinetics ◽  
Atrial Myocytes ◽  
Whole Cell ◽  
Whole Cell Patch Clamp ◽  
Potent Inhibition ◽  
Voltage Dependent ◽  
K Current

Ba2+ is widely used as a tool in patch-clamp studies because of its ability to block a variety of K+channels and to pass Ca2+ channels. Its potential ability to block the cardiac transient outward K+ current ( I to) has not been clearly documented. We performed whole cell patch-clamp studies in canine ventricular and atrial myocytes. Extracellular application of Ba2+ produced potent inhibition of I to with an IC50 of ∼40 μM. The effects were voltage independent, and the inactivation kinetics were not altered by Ba2+. The potency of Ba2+ was ∼10 times higher than that of 4-aminopyridine (a selective I to blocker with an IC50 of 430 μM) under identical conditions. By comparison, Ba2+blockade of the inward rectifier K+ current was voltage dependent; the IC50 was ∼20 times lower (2.5 μM) than that for I to when determined at −100 mV and was comparable to I to as determined at −60 mV (IC50 = 26 μM). Ba2+ concentrations of ≤1 mM or higher failed to block ultrarapid delayed rectifier K+ current. Our data suggest that Ba2+ can be considered a potent blocker of I to.

scholarly journals Two Arginines in the Cytoplasmic C-terminal Domain Are Essential for Voltage-dependent Regulation of A-type K+ Current in the Kv4 Channel Subfamily

2003 ◽  
Vol 279 (7) ◽  
pp. 5450-5459 ◽  
Author(s):  
Noriyuki Hatano ◽  
Susumu Ohya ◽  
Katsuhiko Muraki ◽  
Robert B. Clark ◽  
Wayne R. Giles ◽  
...  
Keyword(s):  
Terminal Domain ◽  
Type K ◽  
Voltage Dependent ◽  
K Current

scholarly journals The Effectiveness in Activating M-Type K+ Current Produced by Solifenacin ([(3R)-1-azabicyclo[2.2.2]octan-3-yl] (1S)-1-phenyl-3,4-dihydro-1H-isoquinoline-2-carboxylate): Independent of Its Antimuscarinic Action

2021 ◽  
Vol 22 (22) ◽  
pp. 12399
Author(s):  
Hsin-Yen Cho ◽  
Tzu-Hsien Chuang ◽  
Sheng-Nan Wu
Keyword(s):  
Single Channel ◽  
Ionic Currents ◽  
Reaction Scheme ◽  
Gh3 Cells ◽  
Whole Cell ◽  
Type K ◽  
Cell Current ◽  
K Current ◽  
Subsequent Addition ◽  
Whole Cell Current

Solifenacin (Vesicare®, SOL), known to be a member of isoquinolines, is a muscarinic antagonist that has anticholinergic effect, and it has been beneficial in treating urinary incontinence and neurogenic detrusor overactivity. However, the information regarding the effects of SOL on membrane ionic currents is largely uncertain, despite its clinically wide use in patients with those disorders. In this study, the whole-cell current recordings revealed that upon membrane depolarization in pituitary GH3 cells, the exposure to SOL concentration-dependently increased the amplitude of M-type K+ current (IK(M)) with effective EC50 value of 0.34 μM. The activation time constant of IK(M) was concurrently shortened in the SOL presence, hence yielding the KD value of 0.55 μM based on minimal reaction scheme. As cells were exposed to SOL, the steady-state activation curve of IK(M) was shifted along the voltage axis to the left with no change in the gating charge of the current. Upon an isosceles-triangular ramp pulse, the hysteretic area of IK(M) was increased by adding SOL. As cells were continually exposed to SOL, further application of acetylcholine (1 μM) failed to modify SOL-stimulated IK(M); however, subsequent addition of thyrotropin releasing hormone (TRH, 1 μM) was able to counteract SOL-induced increase in IK(M) amplitude. In cell-attached single-channel current recordings, bath addition of SOL led to an increase in the activity of M-type K+ (KM) channels with no change in the single channel conductance; the mean open time of the channel became lengthened. In whole-cell current-clamp recordings, the SOL application reduced the firing of action potentials (APs) in GH3 cells; however, either subsequent addition of TRH or linopirdine was able to reverse SOL-mediated decrease in AP firing. In hippocampal mHippoE-14 neurons, the IK(M) was also stimulated by adding SOL. Altogether, findings from this study disclosed for the first time the effectiveness of SOL in interacting with KM channels and hence in stimulating IK(M) in electrically excitable cells, and this noticeable action appears to be independent of its antagonistic activity on the canonical binding to muscarinic receptors expressed in GH3 or mHippoE-14 cells.

scholarly journals The calcium-independent transient outward potassium current in isolated ferret right ventricular myocytes. I. Basic characterization and kinetic analysis.

1993 ◽  
Vol 101 (4) ◽  
pp. 571-601 ◽  
Author(s):  
D L Campbell ◽  
R L Rasmusson ◽  
Y Qu ◽  
H C Strauss
Keyword(s):  
Steady State ◽  
Ventricular Myocytes ◽  
Nonlinear Least Squares ◽  
Patch Clamp Technique ◽  
Time Constants ◽  
Whole Cell Patch Clamp ◽  
Voltage Dependent ◽  
Steady State Inactivation ◽  
K Current ◽  
Necessary And Sufficient

Enzymatically isolated myocytes from ferret right ventricles (12-16 wk, male) were studied using the whole cell patch clamp technique. The macroscopic properties of a transient outward K+ current I(to) were quantified. I(to) is selective for K+, with a PNa/PK of 0.082. Activation of I(to) is a voltage-dependent process, with both activation and inactivation being independent of Na+ or Ca2+ influx. Steady-state inactivation is well described by a single Boltzmann relationship (V1/2 = -13.5 mV; k = 5.6 mV). Substantial inactivation can occur during a subthreshold depolarization without any measurable macroscopic current. Both development of and recovery from inactivation are well described by single exponential processes. Ensemble averages of single I(to) channel currents recorded in cell-attached patches reproduce macroscopic I(to) and indicate that inactivation is complete at depolarized potentials. The overall inactivation/recovery time constant curve has a bell-shaped potential dependence that peaks between -10 and -20 mV, with time constants (22 degrees C) ranging from 23 ms (-90 mV) to 304 ms (-10 mV). Steady-state activation displays a sigmoidal dependence on membrane potential, with a net aggregate half-activation potential of +22.5 mV. Activation kinetics (0 to +70 mV, 22 degrees C) are rapid, with I(to) peaking in approximately 5-15 ms at +50 mV. Experiments conducted at reduced temperatures (12 degrees C) demonstrate that activation occurs with a time delay. A nonlinear least-squares analysis indicates that three closed kinetic states are necessary and sufficient to model activation. Derived time constants of activation (22 degrees C) ranged from 10 ms (+10 mV) to 2 ms (+70 mV). Within the framework of Hodgkin-Huxley formalism, Ito gating can be described using an a3i formulation.

Modulation by endogenously released ATP and opioids of chromaffin cell calcium channels in mouse adrenal slices

2011 ◽  
Vol 300 (3) ◽  
pp. C610-C623 ◽  
Author(s):  
A. Hernández ◽  
P. Segura-Chama ◽  
N. Jiménez ◽  
A. G. García ◽  
J. M. Hernández-Guijo ◽  
...  
Keyword(s):  
Calcium Channels ◽  
Chromaffin Cells ◽  
Opiate Receptors ◽  
Tonic Inhibition ◽  
Inactivation Kinetics ◽  
High Threshold ◽  
Patch Clamp Technique ◽  
Whole Cell ◽  
Voltage Dependent ◽  
Patch Configuration

Modulation of high-threshold voltage-dependent calcium channels by neurotransmitters has been the subject of numerous studies in cultures of neurons and chromaffin cells. However, no studies on such modulation exist in chromaffin cells in their natural environment, the intact adrenal medullary tissue. Here we performed such a study in voltage-clamped chromaffin cells of freshly prepared mouse adrenal slices under the whole cell configuration of the patch-clamp technique. The subcomponents of the whole cell inward Ca2+ current ( ICa) accounted for 49% for L-, 28% for N-, and 36% for P/Q-type channels. T-type Ca2+ channels or residual R-type Ca2+ currents were not seen. However, under the perforated-patch configuration, 20% of ICa accounted for a toxin-resistant R-type Ca2+ current. Exogenously applied ATP and methionine-enkephalin (Met-enk) inhibited ICa by 33%. Stop-flow and Ca2+ replacement by Ba2+, which favored the release of endogenous ATP and opioids, also inhibited ICa, with no changes in activation or inactivation kinetics. This inhibition was partially voltage independent and insensitive to prepulse facilitation. Furthermore, in about half of the cells, suramin and naloxone augmented ICa in the absence of exogenous application of ATP/Met-enk. No additional modulation of ICa was obtained after bath application of exogenous ATP and opioids to these already inhibited cells. Augmentation of ICa was also seen upon intracellular dialysis of guanosine 5′-[β-thio]diphosphate (GDPβS), indicating the existence in the intact slice of a tonic inhibition of ICa in resting conditions. These results suggest that in the intact adrenal tissue a tonic inhibition of ICa exists, mediated by purinergic and opiate receptors.

Distinctive Glycinergic Currents With Fast and Slow Kinetics in Thalamus

2006 ◽  
Vol 95 (6) ◽  
pp. 3438-3448 ◽  
Author(s):  
Amer A. Ghavanini ◽  
David A. Mathers ◽  
Hee-Soo Kim ◽  
Ernest Puil
Keyword(s):  
Single Channel ◽  
Glycine Receptor ◽  
Glycine Receptors ◽  
Decay Kinetics ◽  
Time Constants ◽  
Combined Application ◽  
Long Duration ◽  
Slow Kinetics ◽  
Voltage Dependent ◽  
Intermediate Time

We examined functional properties of inhibitory postsynaptic currents (IPSCs) evoked by medial lemniscal stimulation, spontaneous IPSCs (sIPSCs), and single-channel, extrasynaptic currents evoked by glycine receptor agonists or γ-aminobutyric acid (GABA) in rat ventrobasal thalamus. We identified synaptic currents by reversal at ECl and sensitivity to elimination by strychnine, GABAA antagonists, or combined application. Glycinergic IPSCs featured short (about 12 ms) and long (about 80 ms) decay time constants. These fast and slow IPSCs occurred separately with monoexponential decays, or together with biexponential decay kinetics. Glycinergic sIPSCs decayed monoexponentially with time constants, matching fast and slow IPSCs. These findings were consistent with synaptic responses generated by two populations of glycine receptors, localized under different nerve terminals. Glycine, taurine, or β-alanine applied to excised membrane patches evoked short- and long-duration current bursts. Extrasynaptic burst durations resembled fast and slow IPSC time constants. The single, intermediate time constant (about 22 ms) of GABAAergic IPSCs cotransmitted with glycinergic IPSCs approximated the burst duration of extrasynaptic GABAA channels. We noted differences between synaptic and extrasynaptic receptors. Endogenously activated glycine and GABAA receptor channels had higher Cl− permeability than that of their extrasynaptic counterparts. The β-amino acids activated long-duration bursts at extrasynaptic glycine receptors, consistent with a role in detection of ambient taurine or β-alanine. Heterogenous kinetics and permeabilities implicate molecular and functional diversity in thalamic glycine receptors. Fast, intermediate, and slow inhibitory postsynaptic potential decays, mostly attributed to cotransmission by glycinergic and GABAergic pathways, allow for discriminative modulation and integration with voltage-dependent currents in ventrobasal neurons.

scholarly journals Ternary Kv4.2 channels recapitulate voltage-dependent inactivation kinetics of A-type K+channels in cerebellar granule neurons

2008 ◽  
Vol 586 (8) ◽  
pp. 2093-2106 ◽  
Author(s):  
Yimy Amarillo ◽  
Jose A. De Santiago-Castillo ◽  
Kevin Dougherty ◽  
Jonathon Maffie ◽  
Elaine Kwon ◽  
...  
Keyword(s):  
Cerebellar Granule Neurons ◽  
Inactivation Kinetics ◽  
Granule Neurons ◽  
Cerebellar Granule ◽  
K Channels ◽  
Type K ◽  
Dependent Inactivation ◽  
Voltage Dependent ◽  
Kinetics Of

Ca2+ depolarizes adrenal cortical cells through selective inhibition of an ATP-activated K+ current

1998 ◽  
Vol 275 (6) ◽  
pp. C1526-C1537 ◽  
Author(s):  
Juan Carlos Gomora ◽  
John J. Enyeart
Keyword(s):  
Single Channel ◽  
Direct Interaction ◽  
Selective Inhibition ◽  
Membrane Depolarization ◽  
Zona Fasciculata ◽  
Ang Ii ◽  
Inhibitory Peptide ◽  
Cortical Cells ◽  
Whole Cell ◽  
K Current

Bovine adrenal zona fasciculata cells (AZF) express a noninactivating K+ current ( I AC) whose inhibition by adrenocorticotropic hormone and ANG II may be coupled to membrane depolarization and Ca2 +-dependent cortisol secretion. We studied I ACinhibition by Ca2 + and the Ca2 +ionophore ionomycin in whole cell and single-channel patch-clamp recordings of AZF. In whole cell recordings with intracellular (pipette) Ca2 +concentration ([Ca2+]i) buffered to 0.02 μM, I AC reached maximum current density of 25.0 ± 5.1 pA/pF ( n = 16); raising [Ca2+]ito 2.0 μM reduced it 76%. In inside-out patches, elevated [Ca2+]idramatically reduced I AC channel activity. Ionomycin inhibited I AC by 88 ± 4% ( n = 14) without altering rapidly inactivating A-type K+ current. Inhibition of I ACby ionomycin was unaltered by adding calmodulin inhibitory peptide to the pipette or replacing ATP with its nonhydrolyzable analog 5′-adenylylimidodiphosphate. I AC inhibition by ionomycin was associated with membrane depolarization. When [Ca2+]iwas buffered to 0.02 μM with 2 and 11 mM 1,2-bis(2-aminophenoxy)ethane- N, N, N′, N′-tetraacetic acid (BAPTA), ionomycin inhibited I AC by 89.6 ± 3.5 and 25.6 ± 14.6% and depolarized the same AZF by 47 ± 8 and 8 ± 3 mV, respectively ( n = 4). ANG II inhibited I AC significantly more effectively when pipette BAPTA was reduced from 11 to 2 mM. Raising [Ca2+]iinhibits I ACthrough a mechanism not requiring calmodulin or protein kinases, suggesting direct interaction with I AC channels. ANG II may inhibit I AC and depolarize AZF by activating parallel signaling pathways, one of which uses Ca2 + as a mediator.

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