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Cultured melanotrophs of the adult rat pituitary possess a voltage‐activated fast transient outward current.
Author(s) -
Kehl S J
Publication year - 1989
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.1989.sp017583
Subject(s) - cardiac transient outward potassium current , chemistry , tetraethylammonium , time constant , 4 aminopyridine , conductance , biophysics , electrophysiology , endocrinology , patch clamp , medicine , quinidine , repolarization , reversal potential , voltage clamp , potassium channel , membrane potential , potassium , biology , physics , biochemistry , organic chemistry , condensed matter physics , electrical engineering , engineering
1. Whole‐cell voltage‐clamp recordings were made from cultured melanotrophs obtained from adult rats and maintained in vitro using conventional cell culture procedures. 2. The outward current recorded in the presence of Na+ and Ca2+ channel blockers was normally comprised of two components: a slowly activating, slowly inactivating current (IK(s] and a fast transient current (IK(f]. The selective blockade of IK(s) by 20 mM‐tetraethylammonium (TEA+) allowed the properties of IK(f) to be analysed in isolation. 3. The activation threshold for IK(f) was normally between ‐20 and ‐10 mV and the current‐voltage relationship was linear. At positive potentials the decay of IK(f) was well fitted by a single exponential having a time constant of 20‐35 ms. At ‐70 mV recovery from inactivation was best described by a single‐exponential function with a time constant of 20‐40 ms. IK(f) was fully activatable at ‐60 mV and was fully inactivated at ‐10 mV; the half‐inactivation potential was approximately ‐25 mV. 4. Since IK(f) was reduced by raising the external concentration of K+, was blocked by Ba2+ and Cs+, and persisted in Ca2+‐free medium it is attributed to a voltage‐activated K+ conductance. The amplitude of IK(f) was unaffected either by 5 mM‐4‐aminopyridine (4‐AP) or 50 microM‐quinidine. 5. The electrical properties of IK(f) suggest that by affecting the amplitude and/or duration of the action potential IK(f) may modulate Ca2+ influx and consequently hormone release.