scholarly journals T-type Ca2+ channel lowers the threshold of spike generation in the newt olfactory receptor cell.

1996 ◽  
Vol 108 (6) ◽  
pp. 525-535 ◽  
Author(s):  
F Kawai ◽  
T Kurahashi ◽  
A Kaneko
Keyword(s):  
Action Potential ◽  
Olfactory Receptor ◽  
Action Potentials ◽  
Channel Blocker ◽  
Receptor Cell ◽  
Spike Generation ◽  
Current Clamp ◽  
Patch Clamp Technique ◽  
Olfactory Receptor Cell ◽  
Clamp Condition

Mechanisms underlying action potential generation in the newt olfactory receptor cell were investigated by using the whole-cell version of the patch-clamp technique. Isolated olfactory cells had a resting membrane potential of -70 +/- 9 mV. Injection of a depolarizing current step triggered action potentials under current clamp condition. The amplitude of the action potential was reduced by lowering external Na+ concentration. After a complete removal of Na+, however, cells still showed action potentials which was abolished either by Ca2+ removal or by an application of Ca2+ channel blocker (Co2+ or Ni2+), indicating an involvement of Ca2+ current in spike generation of newt olfactory receptor cells. Under the voltage clamp condition, depolarization of the cell to -40 mV from the holding voltage of -100 mV induced a fast transient inward current, which consisted of Na+ (INa) and T-type Ca2+ (ICa.T) currents. The amplitude of ICa,T was about one fourth of that of INa. Depolarization to more positive voltages also induced L-type Ca2+ current (ICa,L). ICa,L was as small as a few pA in normal Ringer solution. The activating voltage of ICa,T was approximately 10 mV more negative than that of INa. Under current clamp, action potentials generated by a least effective depolarization was almost completely blocked by 0.1 mM Ni2+ (a specific T-type Ca2+ channel blocker) even in the presence of Na+. These results suggest that ICa,T contributes to action potential in the newt olfactory receptor cell and lowers the threshold of spike generation.

scholarly journals Ca2+-activated Cl− current in sheep lymphatic smooth muscle

2000 ◽  
Vol 279 (5) ◽  
pp. C1327-C1335 ◽  
Author(s):  
H. M. Toland ◽  
K. D. McCloskey ◽  
K. D. Thornbury ◽  
N. G. McHale ◽  
M. A. Hollywood
Keyword(s):  
Smooth Muscle ◽  
Carboxylic Acid ◽  
Patch Clamp ◽  
Action Potentials ◽  
Channel Blocker ◽  
Equilibrium Potential ◽  
Plateau Phase ◽  
Current Clamp ◽  
Patch Clamp Technique ◽  
Perforated Patch Clamp

Freshly dispersed sheep mesenteric lymphatic smooth muscle cells were studied at 37°C using the perforated patch-clamp technique with Cs+- and K+-filled pipettes. Depolarizing steps evoked currents that consisted ofl-type Ca2+ [ I Ca(L)] current and a slowly developing current. The slow current reversed at 1 ± 1.5 mV with symmetrical Cl− concentrations compared with 23.2 ± 1.2 mV ( n = 5) and −34.3 ± 3.5 mV ( n = 4) when external Cl− was substituted with either glutamate (86 mM) or I− (125 mM). Nifedipine (1 μM) blocked and BAY K 8644 enhanced I Ca(L), the slow-developing sustained current, and the tail current. The Cl− channel blocker anthracene-9-carboxylic acid (9-AC) reduced only the slowly developing inward and tail currents. Application of caffeine (10 mM) to voltage-clamped cells evoked currents that reversed close to the Cl− equilibrium potential and were sensitive to 9-AC. Small spontaneous transient depolarizations and larger action potentials were observed in current clamp, and these were blocked by 9-AC. Evoked action potentials were triphasic and had a prominent plateau phase that was selectively blocked by 9-AC. Similarly, fluid output was reduced by 9-AC in doubly cannulated segments of spontaneously pumping sheep lymphatics, suggesting that the Ca2+-activated Cl− current plays an important role in the electrical activity underlying spontaneous activity in this tissue.

Effects of estrogen on action potential and membrane currents in guinea pig ventricular myocytes

1999 ◽  
Vol 277 (2) ◽  
pp. H826-H833 ◽  
Author(s):  
Seiko Tanabe ◽  
Toshio Hata ◽  
Masayasu Hiraoka
Keyword(s):  
Guinea Pig ◽  
Action Potential ◽  
Action Potentials ◽  
Voltage Dependence ◽  
Ventricular Myocytes ◽  
Membrane Currents ◽  
Patch Clamp Technique ◽  
17Β Estradiol ◽  
Electrophysiological Effects ◽  
Ionic Basis

To explore a possible ionic basis for the prolonged Q-T interval in women compared with that in men, we investigated the electrophysiological effects of estrogen in isolated guinea pig ventricular myocytes. Action potentials and membrane currents were recorded using the whole cell configuration of the patch-clamp technique. Application of 17β-estradiol (10–30 μM) significantly prolonged the action potential duration (APD) at 20% (APD20) and 90% repolarization (APD90) at stimulation rates of 0.1–2.0 Hz. In the presence of 30 μM 17β-estradiol, APD20 and APD90 at 0.1 Hz were prolonged by 46.2 ± 17.1 and 63.4 ± 11.7% of the control ( n = 5), respectively. In the presence of 30 μM 17β-estradiol the peak inward Ca2+ current ( I CaL) was decreased to 80.1 ± 2.5% of the control ( n = 4) without a shift in its voltage dependence. Application of 30 μM 17β-estradiol decreased the rapidly activating component of the delayed outward K+ current ( I Kr) to 63.4 ± 8% and the slowly activating component ( I Ks) to 65.8 ± 8.7% with respect to the control; the inward rectifier K+ current was barely affected. The results suggest that 17β-estradiol prolonged APD mainly by inhibiting the I Kcomponents I Krand I Ks.

Presynaptic Afferent Inhibition of Lobster Olfactory Receptor Cells: Reduced Action-Potential Propagation Into Axon Terminals

1998 ◽  
Vol 80 (2) ◽  
pp. 1011-1015 ◽  
Author(s):  
Matt Wachowiak ◽  
Lawrence B. Cohen
Keyword(s):  
Action Potential ◽  
Olfactory Receptor ◽  
Receptor Cell ◽  
Action Potential Propagation ◽  
Cell Axon ◽  
Axon Terminals ◽  
Olfactory Receptor Cells ◽  
Receptor Cells ◽  
Afferent Inhibition ◽  
Reduced Action

Wachowiak, Matt and Lawrence B. Cohen. Presynaptic afferent inhibition of lobster olfactory receptor cells: reduced action-potential propagation into axon terminals. J. Neurophysiol. 80: 1011–1015, 1998. Action-potential propagation into the axon terminals of olfactory receptor cells was measured with the use of voltage-sensitive dye imaging in the isolated spiny lobster brain. Conditioning shocks to the olfactory nerve, known to cause long-lasting suppression of olfactory lobe neurons, allowed the selective imaging of activity in receptor cell axon terminals. In normal saline the optical signal from axon terminals evoked by a test stimulus was brief (40 ms) and small in amplitude. In the presence of low-Ca2+/high-Mg2+ saline designed to reduce synaptic transmission, the test response was unchanged in time course but increased significantly in amplitude (57 ± 16%, means ± SE). This increase suggests that propagation into receptor cell axon terminals is normally suppressed after a conditioning shock; this suppression is presumably synaptically mediated. Thus our results show that presynaptic inhibition occurs at the first synapse in the olfactory pathway and that the inhibition is mediated, at least in part, via suppression of action-potential propagation into the presynaptic terminal.

scholarly journals Contribution of L-type Ca2+current to electrical activity in sinoatrial nodal myocytes of rabbits

1999 ◽  
Vol 276 (3) ◽  
pp. H1064-H1077 ◽  
Author(s):  
E. Etienne Verheijck ◽  
Antoni C. G. van Ginneken ◽  
Ronald Wilders ◽  
Lennart N. Bouman
Keyword(s):  
Action Potential ◽  
Calcium Current ◽  
Sodium Current ◽  
Delayed Rectifier ◽  
Current Clamp ◽  
Patch Clamp Technique ◽  
Inward Current ◽  
Delayed Rectifier Current ◽  
Diastolic Depolarization ◽  
Recovery From Inactivation

The role of L-type calcium current ( I Ca,L) in impulse generation was studied in single sinoatrial nodal myocytes of the rabbit, with the use of the amphotericin-perforated patch-clamp technique. Nifedipine, at a concentration of 5 μM, was used to block I Ca,L. At this concentration, nifedipine selectively blocked I Ca,L for 81% without affecting the T-type calcium current ( I Ca,T), the fast sodium current, the delayed rectifier current ( I K), and the hyperpolarization-activated inward current. Furthermore, we did not observe the sustained inward current. The selective action of nifedipine on I Ca,L enabled us to determine the activation threshold of I Ca,L, which was around −60 mV. As nifedipine (5 μM) abolished spontaneous activity, we used a combined voltage- and current-clamp protocol to study the effects of I Ca,L blockade on repolarization and diastolic depolarization. This protocol mimics the action potential such that the repolarization and subsequent diastolic depolarization are studied in current-clamp conditions. Nifedipine significantly decreased action potential duration at 50% repolarization and reduced diastolic depolarization rate over the entire diastole. Evidence was found that recovery from inactivation of I Ca,L occurs during repolarization, which makes I Ca,L available already early in diastole. We conclude that I Ca,L contributes significantly to the net inward current during diastole and can modulate the entire diastolic depolarization.

Cyclic GMP evoked calcium transients in olfactory receptor cell growth cones

Neuroreport ◽  
2000 ◽  
Vol 11 (4) ◽  
pp. 677-681 ◽  
Author(s):  
K W. Kafitz ◽  
T Leinders-Zufall ◽  
F Zufall ◽  
C A. Greer
Keyword(s):  
Cell Growth ◽  
Cyclic Gmp ◽  
Olfactory Receptor ◽  
Receptor Cell ◽  
Growth Cones ◽  
Calcium Transients ◽  
Olfactory Receptor Cell
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