Evidence for two K+ currents activated upon hyperpolarization of Paramecium tetraurelia.
Hyperpolarization of voltage-clamped Paramecium tetraurelia in K+ solutions elicits a complex of Ca2+ and K+ currents. The tail current that accompanies a return to holding potential (-40 mV) contains two K+ components. The tail current elicited by a step to -110 mV of greater than or equal to 50-msec duration contains fast-decaying (tau approximately 3.5 msec) and slow-decaying (tau approximately 20 msec) components. The reversal potential of both components shifts by 55-57 mV/10-fold change in external [K+], suggesting that they represent pure K+ currents. The dependence of the relative amplitudes of the two tail currents on duration of hyperpolarization suggests that the slow K+ current activates slowly and is sustained, whereas the fast current activates rapidly during hyperpolarization and then rapidly inactivates. Iontophoretic injection of a Ca2+ chelator, EGTA, specifically reduces slow tail-current amplitude without affecting the fast tail component. Both K+ currents are inhibited by extracellular TEA+ in a concentration-dependent, noncooperative manner, whereas the fast K+ current alone is inhibited by 0.7 mM quinidine.
Preston
R R
RR
Laboratory of Molecular Biology, University of Wisconsin-Madison 53706.
Saimi
Y
Y
Kung
C
C
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D004533:Egtazic Acid / Q000494:pharmacology; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects; D010247:Paramecium / Q000187:drug effects / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism*; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism*; D011802:Quinidine / Q000494:pharmacology; D013757:Tetraethylammonium Compounds / Q000494:pharmacology
D015221:Potassium Channels; D013757:Tetraethylammonium Compounds; D004533:Egtazic Acid; D011802:Quinidine; D011188:Potassium; D002118:Calcium