Transient outward current carried by inwardly rectifying K+ channels in guinea pig ventricular myocytes dialyzed with low-K+ solution.
There have been periodic reports of nonclassic (4-aminopyridine insensitive) transient outward K+ current in guinea pig ventricular myocytes, with the most recent one describing a novel voltage-gated inwardly rectifying type. In the present study, we have investigated a transient outward current that overlaps inward Ca2+ current (I(Ca,L)) in myocytes dialyzed with 10 mM K+ solution and superfused with Tyrode's solution. Although depolarizations from holding potential (Vhp) -40 to 0 mV elicited relatively small inward I(Ca,L) in these myocytes, removal of external K+ or addition of 0.2 mM Ba2+ more than doubled the amplitude of the current. The basis of the enhancement of I(Ca,L) was the suppression of a large transient outward K+ current. Similar enhancement was observed when Vhp was moved to -80 mV and test depolarizations were preceded by short prepulses to -40 mV. Investigation of the time and voltage properties of the outward K+ transient indicated that it was inwardly rectifying and unlikely to be carried by voltage-gated channels. The outward transient was attenuated in myocytes dialyzed with high-Mg2+ solution, accelerated in myocytes dialyzed with 100 microM spermine solution, and abolished with time in myocytes dialyzed with ATP-free solution. These and other findings suggest that the outward transient is a component of classic "time-independent" inwardly rectifying K+ current.
Zhabyeyev
Pavel
P
Department of Physiology and Biophysics, Dalhousie University, Halifax, Nova Scotia, Canada B3H 4H7.
Asai
Tatsuya
T
Missan
Sergey
S
McDonald
Terence F
TF
D000818:Animals; D002118:Calcium / Q000378:metabolism; D006168:Guinea Pigs; D008564:Membrane Potentials / Q000502:physiology*; D032342:Muscle Cells / Q000502:physiology*; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000378:metabolism; D024661:Potassium Channels, Inwardly Rectifying / Q000502:physiology*; D016276:Ventricular Function
D024661:Potassium Channels, Inwardly Rectifying; D011188:Potassium; D002118:Calcium