A model of the action potential and underlying membrane currents in a rabbit atrial cell

1996 ◽  
Vol 271 (4) ◽  
pp. H1666-H1696 ◽  
Author(s):  
D. S. Lindblad ◽  
C. R. Murphey ◽  
J. W. Clark ◽  
W. R. Giles
Keyword(s):  
Action Potential ◽  
Voltage Clamp ◽  
Cell Voltage ◽  
Ionic Currents ◽  
Membrane Currents ◽  
Whole Cell ◽  
Whole Cell Voltage Clamp ◽  
Voltage Dependent ◽  
Atrial Myocyte ◽  
Atrial Cell

We have developed a mathematical model of the rabbit atrial myocyte and have used it in an examination of the ionic basis of the atrial action potential. Available biophysical data have been incorporated into the model to quantify the specific ultrastructural morphology, intracellular ion buffering, and time- and voltage-dependent currents and transport mechanisms of the rabbit atrial cell. When possible, mathematical expressions describing ionic currents identified in rabbit atrium are based on whole cell voltage-clamp data from enzymatically isolated rabbit atrial myocytes. This membrane model is coupled to equations describing Na+, K+, and Ca2+ homeostasis, including the uptake and release of Ca2+ by the sarcoplasmic reticulum and Ca2+ buffering. The resulting formulation can accurately simulate the whole cell voltage-clamp data on which it is based and provides fits to a family of rabbit atrial cell action potentials obtained at 35 degrees C over a range of stimulus rates (0.2–3.0 Hz). The model is utilized to provide a qualitative prediction of the intracellular Ca2+ concentration transient during the action potential and to illustrate the interactions between membrane currents that underlie repolarization in the rabbit atrial myocyte.

Protein kinase C stimulates Ca2+ current in pregnant rat myometrial cells

1994 ◽  
Vol 72 (11) ◽  
pp. 1304-1307 ◽  
Author(s):  
Keiichi Shimamura ◽  
Masumi Kusaka ◽  
Nicholas Sperelakis
Keyword(s):  
Protein Kinase C ◽  
Protein Kinase ◽  
Voltage Clamp ◽  
Cell Voltage ◽  
Pregnant Rat ◽  
Whole Cell ◽  
Myometrial Cells ◽  
Kinase C ◽  
Whole Cell Voltage Clamp ◽  
Voltage Dependent

The factors that regulate the voltage-dependent Ca2+ channels in pregnant uterine smooth muscle cells have not been elucidated, including any roles for protein kinase C (PKC). Therefore, the role of PKC in the regulation of the slow (L type) Ca2+ channels was examined in myometrial cells isolated from late pregnant (18–19 day) rat uterus, using the nystatin-perforated whole-cell voltage clamp. A PKC activator, phorbol 12, 13-dibutyrate (PDB), increased the L-type Ca2+ current (ICa(L)). Bath application of PDB (0.03 and 0.3 μM) increased the peak amplitude of ICa(L) by 21 ± 14% (n = 6) and 37 ± 8% (n = 9, p < 0.01), respectively. PDB did not change the holding current or shift the current–voltage relationship for ICa(L). The PKC inhibitors, H-7 (20 μM) or staurosporine (10 nM), reversed the effect of PDB. These results indicate that PKC may play a role in regulating Ca2+ channel function in pregnant rat myometrial cells and, therefore, may be involved in control of uterine contraction.Key words: protein kinase C, phorbol ester, calcium current, myometrial cell, nystatin-perforated patch, whole-cell voltage clamp.

Oxytocin induces an inward current in pregnant rat myometrial cells

1994 ◽  
Vol 72 (7) ◽  
pp. 759-763 ◽  
Author(s):  
Keiichi Shimamura ◽  
Masumi Kusaka ◽  
Nicholas Sperelakis
Keyword(s):  
Smooth Muscle ◽  
Voltage Clamp ◽  
Cell Voltage ◽  
Induced Current ◽  
Pregnant Rat ◽  
Whole Cell ◽  
Inward Current ◽  
Uterine Smooth Muscle ◽  
Whole Cell Voltage Clamp ◽  
Voltage Dependent

The effects of oxytocin (OT) on holding current were studied in uterine smooth muscle cells freshly isolated from the longitudinal layer of 18–20 day pregnant rats, using the nystatin method of whole-cell voltage clamp. As we previously reported, the voltage-dependent Ca2+ current (L type) was partially inhibited by OT (about 30% inhibition at 1 μM). When the cells were held at the holding potential (HP) of −60 mV and the holding current was monitored, OT induced an inward current. The amplitude of this OT-induced current was 72 ± 26 pA (n = 27). When the cell was held at more positive potentials (HP 0 or +40 mV), the OT-induced current reversed direction, becoming outward. This current usually was long lasting (74% of cells responding to OT); a transient current was observed in 26% of the cells. In the absence of either Na+ or Ca2+ in the bath solution, OT induced an inward current (at HP −60 mV). However, the OT-induced current was absent when both of these ions were omitted from the bath. These results suggest that OT induces an inward current through receptor-activated nonselective cation channels. The resulting increase of intracellular Ca2+ may contribute to the inhibition of voltage-dependent Ca2+ current produced by OT. This OT-induced current may also play an important role for membrane depolarization and accompanying contraction produced by OT in pregnant rat myometrium.Key words: oxytocin receptor activated channel, uterine smooth muscle, pregnant rat myometrium, holding current, whole-cell voltage clamp.

Developmental change in fast Na channel properties in embryonic chick ventricular heart cells

1995 ◽  
Vol 73 (10) ◽  
pp. 1475-1484 ◽  
Author(s):  
Hideaki Sada ◽  
Takashi Ban ◽  
Takeshi Fujita ◽  
Yoshio Ebina ◽  
Nicholas Sperelakis
Keyword(s):  
Steady State ◽  
Voltage Clamp ◽  
Time Constant ◽  
Voltage Dependence ◽  
Cell Voltage ◽  
Developmental Changes ◽  
Heart Cells ◽  
Embryonic Chick ◽  
Whole Cell ◽  
Whole Cell Voltage Clamp

To assess developmental changes in kinetic properties of the cardiac sodium current, whole-cell voltage-clamp experiments were conducted using 3-, 10-, and 17-day-old embryonic chick ventricular heart cells. Experimental data were quantified according to the Hodgkin–Huxley model. While the Na current density, as examined by the maximal conductance, drastically increased (six- to seven-fold) with development, other current–voltage parameters remained unchanged. Whereas the activation time constant and the steady-state activation characteristics were comparable among the three age groups, the voltage dependence of the inactivation time constant and the steady-state inactivation underwent a shift in the voltage dependence toward negative potentials during embryonic development. Consequently, the steady-state (window current) conductance, which was sufficient to induce automatic activity in the young embryos, was progressively reduced with age.Key words: cardiac electrophysiology, whole-cell voltage-clamp experiments, fast Na currents, heart, development, developmental changes.

Effects of Hyposmolar Solutions on Membrane Currents of Hippocampal Interneurons and Mossy Cells In Vitro

1998 ◽  
Vol 79 (2) ◽  
pp. 1108-1112 ◽  
Author(s):  
Scott C. Baraban ◽  
Philip A. Schwartzkroin
Keyword(s):  
Voltage Clamp ◽  
Hippocampal Slices ◽  
Cell Voltage ◽  
Potassium Currents ◽  
Membrane Currents ◽  
Excitatory Postsynaptic Currents ◽  
Whole Cell ◽  
Mossy Cells ◽  
Postsynaptic Currents

Baraban, Scott C. and Philip A. Schwartzkroin. Effects of hyposmolar solutions on membrane currents of hippocampal interneurons and mossy cells in vitro. J. Neurophysiol. 79: 1108–1112, 1998. Whole cell voltage-clamp recordings in rat hippocampal slices were used to investigate the effect of changes in extracellular osmolarity on voltage-activated potassium currents. Currents were evoked from oriens/alveus (O/A) interneurons, hilar interneurons, and mossy cells. Hyposmolar external solutions produced a significant potentiation of K+ current recorded from O/A and hilar interneurons, but not from mossy cells. Hyposmolar solutions also dramatically potentiated the spontaneous excitatory postsynaptic currents recorded from mossy cells. These results suggest that hippocampal excitability can be modulated by the complex actions exerted by changes in extracellular osmolarity.

A-current in rat globus pallidus: A whole-cell voltage clamp study on acutely dissociated neurons

1992 ◽  
Vol 144 (1-2) ◽  
pp. 4-8 ◽  
Author(s):  
Alessandro Stefani ◽  
Paolo Calabresi ◽  
Nicola B. Mercuri ◽  
Giorgio Bernardi
Keyword(s):  
Voltage Clamp ◽  
Globus Pallidus ◽  
Cell Voltage ◽  
Whole Cell ◽  
Whole Cell Voltage Clamp ◽  
Clamp Study ◽  
A Current

Stimulation of Ca2+ current by phorbol esters in rat myometrial cells is dependent on intracellular Ca2+ concentration

1996 ◽  
Vol 8 (8) ◽  
pp. 1147 ◽  
Author(s):  
M Kusaka ◽  
N Sperelakis
Keyword(s):  
Protein Kinase C ◽  
Protein Kinase ◽  
Voltage Clamp ◽  
Phorbol Esters ◽  
Cell Voltage ◽  
Muscle Cells ◽  
Whole Cell ◽  
Perforated Patch ◽  
Kinase C ◽  
Whole Cell Voltage Clamp

The effects of phorbol esters on the L-type Ca2+ current (ICa(L)) were investigated using nystatin-perforated patch and standard whole-cell voltage clamp in uterine smooth muscle cells isolated from late-pregnant rats. Using nystatin-perforated patch to maintain the integrity of the cytosol components, phorbol 12-myristate 13-acetate (PMA, 300 nM) increased ICa(L). When the standard whole-cell voltage clamp was used, the effect of PMA was dependent on the Ca2+ concentration in the pipette solution: PMA enhanced ICa(L) at pCa 6 and pCa 7 but not at pCa 10 or pCa 8. The effect of PMA was reversed by a selective inhibitor of protein kinase C, calphostin-C (500 nM). It is concluded that phorbol esters stimulate ICa(L) in uterine muscle cells and that the isoform of protein kinase C involved in this effect is Ca2+ dependent. This mechanism may be involved in the regulation of uterine contraction during pregnancy.

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