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Am J Physiol Endocrinol Metab 261: E66-E75, 1991;
0193-1849/91 $5.00
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AJP - Endocrinology and Metabolism, Vol 261, Issue 1 E66-E75, Copyright © 1991 by American Physiological Society

ARTICLES

Evidence for a delayed rectifier-like potassium current in the clonal rat pituitary cell line GH3

S. M. Simasko
Department of Physiology, School of Medicine, State University of New York, Buffalo 14214.

Whole cell patch-clamp techniques were used to investigate voltage-dependent potassium currents in the clonal rat pituitary cell line GH3. Inactivation of the voltage-dependent potassium current was best fit by two time constants (50-80 ms and 2-3 s) plus a sustained value. These components of inactivation could be separated based on their voltage-dependent properties and pharmacological sensitivity to 10 mM tetraethylammonium (TEA) and 5 mM 4-aminopyridine (4-AP). The fast component begins to activate around -50 mV, is half-maximally activated at -19 mV, is 50% inactivated at -55 mV, and is sensitive to 4-AP but insensitive to TEA. The slow component begins to activate at around -10 mV, is half-maximally activated at +4 mV, is 50% inactivated at -23 mV, and is sensitive to both TEA and 4-AP. The sustained component is apparent by 0 mV but has not yet reached half-maximal activation at +57 mV. It is somewhat sensitive to TEA but relatively resistant to 4-AP. In the presence of TEA it was found that the fast-inactivating component actually inactivated in a biphasic manner with time constants of approximately 50 and 500 ms. From the properties of these components it is concluded that at least three distinct voltage-dependent potassium channel types exist in GH3 cells as follows: an A-like current (fast-inactivating component), a delayed rectifier-like current (slow-inactivating component), and the voltage-dependent properties of calcium-dependent potassium channels (the sustained component).


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