Joint voltage- and calcium dependent inactivation of Ca channels in frog atrial myocardium.
Ca currents have been measured from frog atrial myocardium by use of a double sucrose gap voltage clamp technique. Ca inward currents could be separated from overlapping outward currents by means of application of 10 mM 4-aminopyridine and an intracellular Cs-load. The inactivation process of the Ca currents could be separated into two parts: a fast Ca-dependent inactivation and a slow voltage-dependent inactivation. The time constant of the fast decay of the Ca currents was decreased due to increased external Ca concentrations and was U-shaped depending on the membrane potential. As indicated by twin pulse experiments inactivation of a test current following a conditioning current could be increased by increasing the charge inwardly transported during the conditioning current. Long-lasting prepulses being too weak to activate any inward current could also inactivate the test current. Recorded by a prepulse protocol steady-state inactivation curves were described by a half maximum inactivation at -36.7 mV and a slope of 4.2 mV. All the results refer on a joint voltage and calcium dependent inactivation controlling the inwardly transported Ca via the Ca channels.
D000818:Animals; D002118:Calcium / Q000502:physiology*; D066298:In Vitro Techniques; D007473:Ion Channels / Q000502:physiology*; D008564:Membrane Potentials / Q000187:drug effects; D008954:Models, Biological; D009206:Myocardium / Q000378:metabolism*; D011189:Potassium Chloride / Q000494:pharmacology; D011893:Rana esculenta
D007473:Ion Channels; D011189:Potassium Chloride; D002118:Calcium