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Ion selectivity and gating of small conductance Ca(2+)‐activated K+ channels in cultured rat adrenal chromaffin cells.
Author(s) -
Park Y B
Publication year - 1994
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.1994.sp020463
Subject(s) - apamin , chemistry , conductance , tetraethylammonium , depolarization , gating , reversal potential , chromaffin cell , membrane potential , patch clamp , biophysics , analytical chemistry (journal) , methylamine , ion , adrenal medulla , potassium , calcium , endocrinology , biochemistry , chromatography , catecholamine , physics , receptor , organic chemistry , biology , condensed matter physics , medicine
1. The ion selectivity and gating of apamin‐sensitive, small conductance Ca(2+)‐activated K+ (SK) channels were studied in cultured rat adrenal chromaffin cells using patch clamp techniques. 2. The amplitude of slow tail currents showed a bell‐shaped dependence on depolarization potentials. Slow tail currents were abolished in a Ca(2+)‐free external solution or by adding 100 microM Cd2+ to the external solution. Reversal potentials followed the predictions of the Nernst equation for a K+ electrode. 3. Slow tail currents were largely blocked by external application of apamin (dissociation constant, Kd, 4.4 nM), (+)‐tubocurarine (Kd, 20 microM), and tetraethylammonium (Kd, 5.4 mM). 4. The relative permeability (PX/PK, where X may be any one of the ions listed) of SK channels was: Tl+ (1.87) > K+ (1.0) > Rb+ (0.81) > Cs+ (0.16) > NH4+ (0.11). Na+, Li+ and methylamine were not measurably permeant (PX/PK < 0.005). Open SK channels seem to have an effective pore diameter of 0.34‐0.38 nm. The relative conductance (gX/gK) was: Tl+ (1.29) > K+ (1.0) > Rb+ (0.85) > Cs+ (0.45) approximately NH4+ (0.44). 5. With mixtures of Tl+ and K+, SK channels showed anomalous mole‐fraction behaviour. 6. Ca2+ dependence of SK channel gating was studied using inside‐out macropatches. The [Ca2+] required for half‐maximal activation and the Hill coefficient were 0.69 microM and 1.7, respectively, and independent of membrane potentials. 7. Single‐channel conductance was 13‐14 pS (160 mM K+).