ISSN:
1432-1424
Keywords:
inward rectification
;
voltage-dependent K+ current
;
Ca2+-dependent K+ current
;
Paramecium
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Chemistry and Pharmacology
Notes:
Summary Hyperpolarization of voltage-clampedParamecium 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 ≥50-msec duration contains fast-decaying (τ≈3.5 msec) and slow-decaying (τ≈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 0.7mm quinidine.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01869104
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