Potassium channels in cultured bovine adrenal chromaffin cells.

Abstract

SUMMARY1. K channels of bovine adrenal chromaffin cells were studied using patch-clamp techniques.2. Whole-cell K currents measured near + 10 mV were much larger in 1 mM-external Ca than in Ca-free saline. Noise analysis suggested that this Ca-dependent current was carried by a large unitary conductance channel, called BK channel, which was previously described in inside-out patches (Marty, 1981).3. The Ca-dependent K current near + 10 mV declined with time due to 'run-down' of Ca channels. At the same time, a fraction of the outward current observed above + 50 mV was also eliminated. This outward current component probably represents K efflux through Ca channels.4. Whole-cell Ca-dependent K currents were studied using various Ca buffers.EGTA buffers were surprisingly inefficient: in order to block the current entirely, it was necessary to use an isotonic EGTA solution and to increase internal pH. 1 ,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA) was at least five times more efficient than EGTA.5. In isolated patches three types of single-channel K currents were observed. Under normal ionic conditions (140 mM-K inside, 140 mM-Na outside), the unitary conductances measured between -20 and +40 mV were 96 pS, 18 pS and 8 pS. The 96 pS channels are the Ca-dependent BK channels.6. 18 pS and 8 pS channels were both activated and then inactivated by membrane depolarization. Both displayed complex kinetics; single-channel currents were grouped in bursts. Activation and inactivation kinetics were faster for the 18 pS channel (therefore termed FK channel, for fast K channel) than for the 8 pS channel (SK channel, for slow or small amplitude channel). The voltage dependence ofopening probability was steeper for the FK channel as compared to the SK channel.

Somato-dendritic mechanisms underlying the electrophysiological properties of hypothalamic magnocellular neuroendocrine cells: A multicompartmental model study

“…Ca 2+ -activated K + currents: The model includes two Ca 2+ -activated K + currents mediated by SK and BK channels (Marty 1981;Marty and Neher 1985;Vergara et al 1998). Activation of the SK channels is voltage independent and highly sensitive to intracellular Ca 2+ (Hille 2001;Sah and Davies 2000); BK channel activation is both voltage-and Ca 2+ -dependent (Vergara et al 1998;Dopico et al 1999).…”

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

“…Colocalization remains less certain in hair cells from other species (Art et al, 1995). In the neurons of Helix, only a subset of Ca 2ϩ -dependent K ϩ channels are coupled to Ca 2ϩ channels (Gola and Crest, 1993), and, in bovine chromaffin cells, BAPTA is more effective than EGTA in suppressing Ca 2ϩ -activated K ϩ current (Marty and Neher, 1985), suggesting that at least some of the Ca 2ϩ -activated K ϩ channels are colocalized with Ca 2ϩ channels.…”

Pharmacological evidence for the possible involvement of repetitive action potentials in facilitation by GABA of catecholamine secretion in bovine adrenal chromaffin cells

“…Both Na+ and Ca2+ influx are opposed by the outward movement of K+. An electrophysiological study demonstrated the presence of several types of K+ channels in chromaffin cells and its inhibition by TEA (Marty & Neher, 1985). Further, Kidokoro & Ritchie (1980) explained the stimulatory action of TEA on KCI-induced CA secretion with regard to the action potential, and suggested that TEA is only effective on the portion of CA secretion which is mediated by spike activity.…”