scholarly journals Sodium and calcium currents in dispersed mammalian septal neurons.

1991 ◽  
Vol 97 (2) ◽  
pp. 303-320 ◽  
Author(s):  
A Castellano ◽  
J López-Barneo
Keyword(s):  
Time Constant ◽  
Time Course ◽  
Calcium Currents ◽  
Closing Time ◽  
Patch Clamp Technique ◽  
Average Value ◽  
Time To Peak ◽  
Time Courses ◽  
Fast Activation ◽  
Septal Neurons

Voltage-gated Na+ and Ca2+ conductances of freshly dissociated septal neurons were studied in the whole-cell configuration of the patch-clamp technique. All cells exhibited a large Na+ current with characteristic fast activation and inactivation time courses. Half-time to peak current at -20 mV was 0.44 +/- 0.18 ms and maximal activation of Na+ conductance occurred at 0 mV or more positive membrane potentials. The average value was 91 +/- 32 nS (approximately 11 mS cm-2). At all membrane voltages inactivation was well fitted by a single exponential that had a time constant of 0.44 +/- 0.09 ms at 0 mV. Recovery from inactivation was complete in approximately 900 ms at -80 mV but in only 50 ms at -120 mV. The decay of Na+ tail currents had a single time constant that at -80 mV was faster than 100 microseconds. Depolarization of septal neurons also elicited a Ca2+ current that peaked in approximately 6-8 ms. Maximal peak Ca2+ current was obtained at 20 mV, and with 10 mM external Ca2+ the amplitude was 0.35 +/- 0.22 nA. During a maintained depolarization this current partially inactivated in the course of 200-300 ms. The Ca2+ current was due to the activity of two types of conductances with different deactivation kinetics. At -80 mV the closing time constants of slow (SD) and fast (FD) deactivating channels were, respectively, 1.99 +/- 0.2 and 0.11 +/- 0.03 ms (25 degrees C). The two kinds of channels also differed in their activation voltage, inactivation time course, slope of the conductance-voltage curve, and resistance to intracellular dialysis. The proportion of SD and FD channels varied from cell to cell, which may explain the differential electrophysiological responses of intracellularly recorded septal neurons.

Characterization of voltage-dependent calcium currents in mouse motoneurons

1992 ◽  
Vol 68 (1) ◽  
pp. 85-92 ◽  
Author(s):  
M. Mynlieff ◽  
K. G. Beam
Keyword(s):  
Voltage Dependence ◽  
Low Voltage ◽  
Calcium Currents ◽  
Patch Clamp Technique ◽  
Maximal Amplitude ◽  
Time To Peak ◽  
Whole Cell Patch Clamp ◽  
Voltage Dependent ◽  
Channel Currents

1. Calcium channel currents were measured with the whole-cell patch clamp technique in cultured, identified mouse motoneurons. Three components of current were operationally defined on the basis of voltage dependence, kinetics, and pharmacology. 2. Test potentials to -50 mV or greater (10 mM external Ca2+) elicited a low-voltage activated T-type current that was transient (decaying to baseline in less than 200 ms) and had a relatively slow time to peak (20-50 ms). A 1-s prepulse to -45 mV produced approximately half-maximal inactivation of this T current. 3. Two high-voltage activated (HVA) components of current (1 transient and 1 sustained) were activated by test potentials to -20 mV or greater (10 mM external Ca2+). A 1-s prepulse to -35 mV produced approximately half-maximal inactivation of the transient component without affecting the sustained component. 4. When Ba2+ was substituted for Ca2+ as the charge carrier, activation of the HVA components was shifted in the hyperpolarizing direction, and the relative amplitude of the transient HVA component was reduced. 5. Amiloride (1-2 mM) caused a reversible, partial block of the T current without affecting the HVA components. 6. The dihydropyridine agonist isopropyl 4-(2,1,3-benzoxadiazol-4-yl)-1,4-dihydro-2,6-dimethyl-5-nitro-3- pyridine-carboxylate [(+)-SDZ 202-791, 100 nM-1 microM)] shifted the activation of the sustained component of HVA current to more negative potentials and increased its maximal amplitude. Additionally, (+)-SDZ 202-791 caused the appearance of a slowed component of tail current.(ABSTRACT TRUNCATED AT 250 WORDS)

Force measurements from voltage-clamped guinea pig ventricular myocytes

1990 ◽  
Vol 258 (2) ◽  
pp. H452-H459 ◽  
Author(s):  
N. Shepherd ◽  
M. Vornanen ◽  
G. Isenberg
Keyword(s):  
Guinea Pig ◽  
Time Course ◽  
Ventricular Myocytes ◽  
Isometric Force ◽  
Contractile Force ◽  
Patch Clamp Technique ◽  
Thin Glass ◽  
Tonic Component ◽  
Time To Peak ◽  
Whole Cell Patch Clamp

We describe the first observations of isolated mammalian guinea pig ventricular myocytes that combine measurements of contractile force with the voltage-clamp method. The myocytes were attached by poly-L-lysine to the beveled ends of a pair of thin glass rods having a compliance of 0.76 m/N. The contractile force of a cell caused a 1- to 3-microm displacement of the rods; the motion of which was converted to an output voltage by phototransistors. By the use of the whole cell patch-clamp technique, the cells were depolarized at 1 Hz with 200-ms-long clamp pulses from -45 to +5 mV (35 degrees C, 3.6 mM CaCl2). Isometric force began after a latency of 7 +/- 2 ms, peaked at 93 +/- 21 ms, and relaxed (90%) at 235 +/- 63 ms. The time course of force was always faster than that of isotonic shortening (time to peak 154 +/- 18 ms). With 400-ms-long depolarizations, a tonic component was recorded as either sustained force or sustained shortening that decayed on repolarization. Substitution of Ca by Sr in the bath increased the inward current through Ca channels but slowed down the time course of force development. The results are consistent with the hypothesis that activator calcium derives mainly from internal stores and that Ca release needs Ca entry through channels.

Average but not continuous speed match between motoneurons and muscle units of rat tibialis anterior

1993 ◽  
Vol 70 (4) ◽  
pp. 1300-1306 ◽  
Author(s):  
R. Bakels ◽  
D. Kernell
Keyword(s):  
Tibialis Anterior ◽  
Time Course ◽  
Muscle Fibers ◽  
Total Duration ◽  
Medial Gastrocnemius ◽  
Tetanic Force ◽  
Time To Peak ◽  
Time Courses ◽  
Isometric Twitch ◽  
Fatigue Sensitivity

1. Properties of single motoneuron/muscle-unit combinations were determined for tibialis anterior (TA) in rats anesthetized with pentobarbital. The TA observations were systematically compared with those obtained earlier by the use of the same techniques from rat medial gastrocnemius (MG). 2. TA motoneurons were investigated with regard to afterhyperpolarization (AHP; total duration 32-74 ms, amplitude 0.39-4.96 mV) and axonal conduction velocity (41-79 m/s). TA muscle-unit measurements included the time course of the isometric twitch (time-to-peak force 10.8-18.0 ms; total duration 42-92 ms), the maximum tetanic force (22-217 mN), and a measure of fatigue sensitivity (fatigue index 5-100%). The range of twitch and AHP durations ("speed range") was markedly smaller in the present TA material than for MG. 3. The mean duration of the TA motoneuronal AHP (49 +/- 8 ms, mean +/- SD) was close to that of its muscle-unit twitch (56 +/- 12 ms). Thus an "average" speed match existed between TA motoneurons and their muscle fibers. 4. For TA there was no correlation between the time courses of AHP and twitch. Thus there was for TA no "continuous" speed match between the motoneurons and their muscle fibers. 5. For TA twitches or AHPs studied separately, there was a significant correlation between different time course measures. Furthermore, compared with TA units having relatively fast twitches, those with slower twitches tended to show 1) a smaller maximum tetanic force and 2) a greater AHP amplitude. Fatigue-resistant units tended to have slower twitches than fatigue-sensitive ones.(ABSTRACT TRUNCATED AT 250 WORDS)

Voltage-dependent K+ current in capillary endothelial cells isolated from guinea pig heart

1999 ◽  
Vol 277 (1) ◽  
pp. H119-H127 ◽  
Author(s):  
Michael Dittrich ◽  
Jürgen Daut
Keyword(s):  
Guinea Pig ◽  
Time Course ◽  
Single Channel ◽  
Patch Clamp Technique ◽  
Guinea Pig Heart ◽  
Potential Oscillations ◽  
Time To Peak ◽  
Voltage Dependent ◽  
Capillary Endothelial Cells ◽  
Single Channel Currents

Capillary fragments were isolated from guinea pig hearts, and their electrical properties were studied using the perforated-patch and cell-attached mode of the patch-clamp technique. A voltage-dependent K+ current was discovered that was activated at potentials positive to −20 mV and showed a sigmoid rising phase. For depolarizing voltage steps from −128 to +52 mV, the time to peak was 71 ± 5 ms (mean ± SE) and the amplitude of the current was 3.7 ± 0.5 pA/pF in the presence of 5 mM external K+. The time course of inactivation was exponential with a time constant of 7.2 ± 0.5 s at +52 mV. The current was blocked by tetraethylammonium (inhibitory constant ∼3 mM) but was not affected by charybdotoxin (1 μM) or apamin (1 μM). In the cell-attached mode, depolarization-activated single-channel currents were found that inactivated completely within 30 s; the single-channel conductance was 12.3 ± 2.4 pS. The depolarization-activated K+current described here may play a role in membrane potential oscillations of the endothelium.

Activity-Dependent [Ca2+]i Changes in Guinea Pig Vagal Motoneurons: Relationship to the Slow Afterhyperpolarization

1997 ◽  
Vol 78 (2) ◽  
pp. 825-834 ◽  
Author(s):  
Nechama Lasser-Ross ◽  
William N. Ross ◽  
Yosef Yarom
Keyword(s):  
Guinea Pig ◽  
Time Constant ◽  
Recovery Time ◽  
Time Course ◽  
Pyramidal Neurons ◽  
Cell Types ◽  
Time To Peak ◽  
Ca1 Region ◽  
Activity Dependent ◽  
Calcium Green

Lasser-Ross, Nechama, William N. Ross, and Yosef Yarom. Activity-dependent [Ca2+]i changes in guinea pig vagal motoneurons: relationship to the slow afterhyperpolarization. J. Neurophysiol. 78: 825–834, 1997. Vagal motoneurons in slices from the guinea-pig brain stem were injected with the fluorescent [Ca2+]i indicators fura-2, furaptra, or Calcium Green-1. Spike-induced fluorescence changes were measured in the soma and dendrites and simultaneously the long-lasting afterhyperpolarization was recorded with a sharp microelectrode in the soma. Na+ spikes or Ca2+ spikes increased [Ca2+]i (measured as a change in indicator fluorescence) in all locations in the soma and dendrites. Each spike in a train of action potentials caused a step increase in fluorescence of about equal amplitude when nonsaturating indicators were used. Peak changes at all locations occurred at the time of the last action potential. Transients measured with low concentrations of Calcium Green-1 or furaptra had a recovery time constant of ∼500–1,500 ms in the cell body. The recovery time course was faster in the dendrites than in the soma. The norepinephrine-sensitive, slow afterhyperpolarization (sAHP) had a time to peak of ∼800 ms and a recovery time constant of 2–5 s, much longer than the recovery time course of the fluorescence changes. Some of these experiments were repeated on pyramidal neurons from the CA1 region of the rat hippocampus with similar results. In both cell types, the data suggest that the time course of neither the rising phase nor the falling phase of the sAHP, nor the underlying conductance, directly reflects the time course of the [Ca2+]i change. The mechanism connecting the parameters remains unclear. One possibility is that an additional second messenger system is involved.

scholarly journals Delays in inactivation development and activation kinetics in myxicola giant axons.

1982 ◽  
Vol 80 (1) ◽  
pp. 83-102 ◽  
Author(s):  
L Goldman ◽  
J L Kenyon
Keyword(s):  
Time Constant ◽  
Time Course ◽  
Series Resistance ◽  
Activation Kinetics ◽  
Time To Peak ◽  
Exponential Decline ◽  
Na Inactivation ◽  
The Difference ◽  
True Property ◽  
Kinetics Of

Na inactivation was studied in Myxicola (two-pulse procedure, 6-ms gap between conditioning and test pulses). Inactivation developed with an initial delay (range 130-817 microseconds) followed by a simple exponential decline (time constant tau c). Delays (deviations from a simple exponential) are seen only for brief conditioning pulses were gNa is slightly activated. Hodgkin-Huxley kinetics with series resistance, Rs, predict deviations from a simple exponential only for conditioning pulses that substantially activate gNa. Reducing INa fivefold (Tris substitution) had no effect on either tau c or delay. Delay in not generated by Rs or by contamination from activation development. The slowest time constant in Na tails is approximately 1 ms (Goldman and Hahin, 1978) and the gap was 6 ms. Shortening the gap to 2 ms had no effect on either tau c or delay. Delay is a true property of the channel. Delay decreased with more positive conditioning potentials, and also decreased approximately proportionally with time to peak gNa during the conditioning pulse, as expected for sequentially coupled activation and inactivation. In a few cases the difference between Na current values for brief conditioning pulses and the tau c exponential could be measured. Difference values decayed exponentially with time constant tau m. The inactivation time course is described by a model that assumes a process with the kinetics of gNa activation as a precursor to inactivation.

Multiple calcium currents in a thyroid C-cell line: biophysical properties and pharmacology

1991 ◽  
Vol 260 (6) ◽  
pp. C1253-C1263 ◽  
Author(s):  
B. A. Biagi ◽  
J. J. Enyeart
Keyword(s):  
Cell Line ◽  
Time Constant ◽  
Calcium Currents ◽  
C Cells ◽  
Patch Clamp Technique ◽  
C Cell ◽  
Dependent Inactivation ◽  
Voltage Dependent ◽  
Rat Thyroid ◽  
Ca2 Channels

The whole cell version of the patch-clamp technique was used to characterize voltage-gated Ca2+ channels in the calcitonin-secreting rat thyroid C-cell line 6-23 (clone 6). Three types of Ca2+ channels could be distinguished based on differences in voltage dependence, kinetics, and pharmacological sensitivity. T-type current was half-maximal at -31 mV, showed steady-state voltage-dependent inactivation that was half-maximal at -57 mV, inactivated with a voltage-dependent time constant that reached a minimum of 20 ms at potentials positive to -20 mV, and deactivated with a single time constant of approximately 2 ms at -80 mV. Reactivation of inactivated channels occurred with a time constant of 1.26 s at -90 mV. T current was selectively blocked by Ni2+ at concentrations between 5 and 50 microM. La3+ and Y3+ blocked the T current at 10- to 20-fold lower concentrations. Dihydropyridine-sensitive L-type current was half-maximal at a test potential of -3 mV and was approximately doubled in size when Ba2+ replaced Ca2+ as the charge carrier. Unlike L-type Ca2+ current in many cells, this current in C-cells displayed little Ca(2+)-dependent inactivation. N-type current was composed of inactivating and sustained components that were inhibited by omega-conotoxin. The inactivating component was half-maximal at +9 mV and could be fitted by two exponentials with time constants of 22 and 142 ms. A slow inactivation of N current with a time constant of 24.9 s was observed upon switching the holding potential from -80 to -40 mV. These results demonstrate that, similar to other neural crest derived cells, thyroid C-cells express multiple Ca2+ channels, including one previously observed only in neurons.

scholarly journals Kinetics of intramembrane charge movement and sodium current in frog node of Ranvier.

1982 ◽  
Vol 79 (4) ◽  
pp. 571-602 ◽  
Author(s):  
J M Dubois ◽  
M F Schneider
Keyword(s):  
Time Constant ◽  
Time Course ◽  
Sodium Current ◽  
Node Of Ranvier ◽  
Charge Movement ◽  
Intramembrane Charge Movement ◽  
Time Courses ◽  
Charge Movements ◽  
Kinetics Of ◽  
Microsecond Pulse

Intramembrane charge movement (Q) and sodium current (INa) were monitored in isolated voltage-clamped frog nodes of Ranvier, ON charge movements (QON) for pulses from the holding potential (-100 mV) to potentials V less than or equal to 0 mV followed single exponential time courses, whereas two exponentials were found for pulses to V greater than or equal to 20 mV. The voltage dependence of both QON and its time constant tauON indicated that the two ON components resolved at V greater than or equal to 20 mV were also present, though not resolvable, for pulses to V less than or equal to 0 mV. OFF charge movements (QOFF) monitored at various potentials were well described by single exponentials. When QOFF was monitored at -30 or -40 mV after a 200-microsecond pulse to +20 mV and QON was monitored at the same potential using pulses directly from -100 mV, tauON/tauOFF = 2.5 +/- 0.3. At a set OFF potential (-90 to -70 mV), tauOFF first increased with increasing duration tON of the preceding pulse to a given potential (0 to +30 mV) and then decreased with further increases in tON. The declining phase of tauOFF followed a time course similar to that of the decline in QOFF with tON. For the same pulse protocol, the OFF time constant tauNa for INA also first increased with tON but then remained constant over the tON interval during which tauOFF and QOFF were declining. After 200- or 300-microsecond pulses to +20, +20, or +50 mV, tauOFF/tauNa at -70 to -90 mV was 1.2 +/- 0.1. Similar tauOFF/tauNa ratios were predicted by channel models having three identical charged gating particles that can rapidly and reversibly form an immobile dimer or trimer after independently crossing the membrane from their OFF to their ON locations.

The use of m-sequences in the analysis of visual neurons: Linear receptive field properties

1997 ◽  
Vol 14 (6) ◽  
pp. 1015-1027 ◽  
Author(s):  
R. C. Reid ◽  
J. D. Victor ◽  
R. M. Shapley
Keyword(s):  
Receptive Field ◽  
Time Course ◽  
Receptive Fields ◽  
Response Dynamics ◽  
Visual Neurons ◽  
Response Properties ◽  
Time To Peak ◽  
M Sequence ◽  
Sequence Method ◽  
Time Courses

AbstractWe have used Sutter's (1987) spatiotemporal m-sequence method to map the receptive fields of neurons in the visual system of the cat. The stimulus consisted of a grid of 16 X 16 square regions, each of which was modulated in time by a pseudorandom binary signal, known as an m-sequence. Several strategies for displaying the m-sequence stimulus are presented. The results of the method are illustrated with two examples. For both geniculate neurons and cortical simple cells, the measurement of first-order response properties with the m-sequence method provided a detailed characterization of classical receptive-field structures. First, we measured a spatiotemporal map of both the center and surround of a Y-cell in the lateral geniculate nucleus (LGN). The time courses of the center responses was biphasic: OFF at short latencies, ON at longer latencies. The surround was also biphasic—ON then OFF—but somewhat slower. Second, we mapped the response properties of an area 17 directional simple cell. The response dynamics of the ON and OFF subregions varied considerably; the time to peak ranged over more than a factor of two. This spatiotemporal inseparability is related to the cell's directional selectivity (Reid et al., 1987, 1991; McLean & Palmer, 1989; McLean et al., 1994). The detail with which the time course of response can be measured at many different positions is one of the strengths of the m-sequence method.

scholarly journals Properties of calcium and potassium currents of clonal adrenocortical cells.

1989 ◽  
Vol 93 (3) ◽  
pp. 495-519 ◽  
Author(s):  
L Tabares ◽  
J Ureña ◽  
J López-Barneo
Keyword(s):  
Time Course ◽  
Outward Current ◽  
Ionic Currents ◽  
Ca Current ◽  
Closing Time ◽  
Patch Clamp Technique ◽  
Adrenocortical Cells ◽  
Activation Threshold ◽  
Activation Kinetics ◽  
K Current

The ionic currents of clonal Y-1 adrenocortical cells were studied using the whole-cell variant of the patch-clamp technique. These cells had two major current components: a large outward current carried by K ions, and a small inward Ca current. The Ca current depended on the activity of two populations of Ca channels, slow (SD) and fast (FD) deactivating, that could be separated by their different closing time constants (at -80 mV, SD, 3.8 ms, and FD, 0.13 ms). These two kinds of channels also differed in (a) activation threshold (SD, approximately -50 mV; FD, approximately -20 mV), (b) half-maximal activation (SD, between -15 and -10 mV; FD between +10 and +15 mV), and (c) inactivation time course (SD, fast; FD, slow). The total amplitude of the Ca current and the proportion of SD and FD channels varied from cell to cell. The amplitude of the K current was strongly dependent on the internal [Ca2+] and was almost abolished when internal [Ca2+] was less than 0.001 microM. The K current appeared to be independent, or only slightly dependent, of Ca influx. With an internal [Ca2+] of 0.1 microM, the activation threshold was -20 mV, and at +40 mV the half-time of activation was 9 ms. With 73 mM external K the closing time constant at -70 mV was approximately 3 ms. The outward current was also modulated by internal pH and Mg. At a constant pCa gamma a decrease of pH reduced the current amplitude, whereas the activation kinetics were not much altered. Removal of internal Mg produced a drastic decrease in the amplitude of the Ca-activated K current. It was also found that with internal [Ca2+] over 0.1 microM the K current underwent a time-dependent transformation characterized by a large increase in amplitude and in activation kinetics.

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