K efflux through inward rectifying K channels in voltage clamped Purkinje fibers.
The 42K efflux was measured in voltage clamped sheep Purkinje fibers. The voltage dependence of the K efflux can be described as N-shaped, showing a negative slope region. At potentials negative to -30mV, the K efflux is largely due to K flowing through a channel which rectifies in the inward direction and which is blocked by external application of 20mM Cs+. At potentials positive to -30mV an outward rectifier dominates the shape of the K efflux-voltage relationship. This component is insensitive to short external application of Cs+. Both components were also found when Na+ was replaced by tetramethylammonium. When the steady-state current-voltage relationship is compared with the K efflux one can conclude that the outward rectifying K flux largely determines the shape of this curve at positive membrane potentials, while the negative slope region of the K efflux correlates with the negative slope of the steady-state current-voltage relation. The K efflux is only slightly enhanced by stimulation of the preparation, corroborating the finding of inward-going rectification of the K channel. A clamp program repetitively activating the positive dynamic current e.g. by alternating the membrane potential between -70 and +10mV, increases the K efflux by about 50% as compared to the efflux measured in steady-state at this positive membrane potential. 4-Aminopyridine suppresses both this extra K efflux and the positive dynamic current. It is concluded that K ions contribute to the positive dynamic current.
D000818:Animals; D002586:Cesium / Q000494:pharmacology; D004558:Electric Stimulation; D006329:Heart Conduction System / Q000378:metabolism*; D007473:Ion Channels / Q000378:metabolism*; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects; D011188:Potassium / Q000378:metabolism*; D011690:Purkinje Fibers / Q000187:drug effects / Q000378:metabolism*; D012756:Sheep
D007473:Ion Channels; D002586:Cesium; D011188:Potassium