Ion selectivity and gating of small conductance Ca(2+)‐activated K+ channels in cultured rat adrenal chromaffin cells.

Abstract

1. The ion selectivity and gating of apamin-sensitive, small conductance Ca2+-activated K+ (SK) respectively, and independent of membrane potentials.

β-Adrenergic Stimulation Selectively Inhibits Long-Lasting L-Type Calcium Channel Facilitation in Hippocampal Pyramidal Neurons

“…The three classes of SK channels cloned, which include SK1, the mRNA for which is present in hippocampal pyramidal neurons, are half-maximally activated by ϳ700 nM Ca (Köhler et al, 1996). This value is similar to the Ca sensitivity of the apamin-sensitive SK channel found in rat adrenal chromaffin cells (K 0.5 , ϳ800 nM) (Park, 1994). Therefore, the measured intracellular calcium transients are probably too small to account for activation of SK channels that underlie generation of the slow AHP.…”

[Ca2+]iElevations Detected by BK Channels during Ca2+Influx and Muscarine-Mediated Release of Ca2+from Intracellular Stores in Rat Chromaffin Cells

“…Activation of both types of current is observed with depolarizing steps that produce Ca 2ϩ influx via voltage-dependent Ca 2ϩ channels (Neely and Lingle, 1992a) and with the release of intracellular calcium by agents such as muscarine and caffeine (Neely and Lingle, 1992b;Herrington et al, 1995). Over the range of physiological potentials (Ϫ60 to ϩ50 mV), chromaffin cell SK channels are more sensitive to Ca 2ϩ than BK channels: maximal activation of SK channels occurs at [Ca 2ϩ ] i of 2-4 M (Park, 1994), whereas maximal activation of BK channels at 4 M [Ca 2ϩ ] i occurs only at membrane potentials of ϩ90 mV and above (see Fig. 3).…”

“…Rat chromaffin cells display two major categories of Ca 2ϩ -dependent K ϩ current: one current results from voltagedependent, large conductance BK channels (Neely and Lingle, 1992a), and the other results from voltage-independent, small conductance SK channels that are sensitive to apamin (Neely and Lingle, 1992a;Park, 1994). Activation of both types of current is observed with depolarizing steps that produce Ca 2ϩ influx via voltage-dependent Ca 2ϩ channels (Neely and Lingle, 1992a) and with the release of intracellular calcium by agents such as muscarine and caffeine (Neely and Lingle, 1992b;Herrington et al, 1995).…”

Characterization of Ca2+‐activated 86Rb+ fluxes in rat C6 glioma cells: a system for identifying novel IKCa‐channel toxins

“…BKCa channels are typically blocked by charybdotoxin, a peptide toxin (Mr 4300 Da) isolated from the venom of the Israeli scorpion Leiurus quinquestriatus hebraeus (Miller et al, 1985; al., 1988; and iberiotoxin (Mr 4300 Da) isolated from the venom of the Indian scorpion, Mesobuthus tamulus (Galvez et al, 1990). SKCa channels on the other hand, are specifically blocked by apamin (Blatz & Magleby, 1986;Capiod & Ogden, 1989;Park, 1994), an octadecapeptide (Mr 2000 Da) isolated from the venom of the European honey bee, Apis mellifera (Gauldie et al, 1976;. IKCa channels have a pharmacology that is closer in characteristics to that of BKCa channels, than SKCa channels.…”