Is there an A-type K+ current in guinea pig ventricular myocytes?
A unique transient outward K(+) current (I(to)) has been described to result from the removal of extracellular Ca(2+) from ventricular myocytes of the guinea pig (15). This study addressed the question of whether this current represented K(+)-selective I(to) or the efflux of K(+) via L-type Ca(2+) channels. This outward current was inhibited by Cd(2+), Ni(2+), Co(2+), and La(3+) as well as by nifedipine. All of these compounds were equally effective inhibitors of the L-type Ca(2+) current. The current was not inhibited by 4-aminopyridine. Apparent inhibition of the outward current by extracellular Ca(2+) was shown to result from the displacement of the reversal potential of cation flux through L-type Ca(2+) channels. The current was found not to be K(+) selective but also permeant to Cs(+). The voltage dependence of inactivation of the outward current was identical to that of the L-type Ca(2+) current. It is concluded that extracellular Ca(2+) does not mask an A-type K(+) current in guinea pig ventricular myocytes.
Findlay
Ian
I
Faculté des Sciences, Centre National de la Recherche Scientifique UMR 6542, Université de Tours, France. findlay@univ-tours.fr
D000818:Animals; D002118:Calcium / Q000378:metabolism; D020746:Calcium Channels, L-Type / Q000502:physiology; D002586:Cesium / Q000378:metabolism; D004553:Electric Conductivity; D005110:Extracellular Space / Q000378:metabolism; D006168:Guinea Pigs; D006352:Heart Ventricles; D032383:Myocytes, Cardiac / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism; D015221:Potassium Channels / Q000502:physiology*
D020746:Calcium Channels, L-Type; D015221:Potassium Channels; D002586:Cesium; D011188:Potassium; D002118:Calcium