Properties of single calcium‐activated potassium channels in cultured rat muscle

Abstract

SUMMARY1. Properties of the Ca-activated K channel were studied in excised patches of surface membrane from cultured rat muscle cells using single channel 4. Both the frequency and effective duration of channel openings increased as the intracellular membrane surface was made more positive; the percentage of time spent in the open state increased e-fold for a 15 mV depolarization for low levels of activity.5. The percentage of time spent with 1, 2, .. .n channels open in membrane patches with n channels was described by the binomial distribution, suggesting that the channels opened and shut independently of one another.6. Single channel conductance (144 mM-K on both sides of the membrane) was essentially independent of membrane potential (-50 to + 50 mV) and [Ca]i (0 1 /zM -1 mM), but did increase with temperature, from 100 pS at 1 'C to 300 pS at 37 'C. 7. Channel activity occurred in apparent bursts, with the duration of the apparent bursts increasing with increasing [Ca]1. single channel currents. The reduced conductance state was immediately preceded and followed by a normal conducting state.10. While the kinetics of the Ca-activated K channel appear complex, its large conductance and high Ca and voltage sensitivity suggest that it is uniquely suited to resist depolarizations of the cell membrane potential that are accompanied by increases in intracellular Ca.* To whom reprint requests should be sent.

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

“…The cytosolic free Ca2+ concentration inducing 50% of the maximal current response is typically 350 nM in granulocytes (Varnai et al, 1993). This is in distinction to the Ca2"-sensitivity of BKca channels, which characteristically open either when the cytosolic Ca2+ concentration is several micromolar or at strongly depolarized voltages (Barrett et al, 1982;Hille, 1992).…”

.BETA.-Actions of catecholamines on the K-related currents of the bullfrog atrial muscle.

“…MEECH (1972) first observed the Ca-activated increase of K permeability in Aplysia nerve cells. Studies on Ca-activated K currents have been performed at the single channel level in neurons, smooth muscle, chromaffin cells, and skeletal muscle (MEECH, 1974(MEECH, , 1978THOMPSON, 1977;MIRONNEAU and SAVINEAU, 1980;MARTY, 1981;BARRETT et al, 1982). In cardiac tissues also, ISENBERG (1977a, b) showed the evidence of the Ca-activated K conductance in sheep Purkinje fibers.…”

Charybdotoxin block of single Ca2+-activated K+ channels. Effects of channel gating, voltage, and ionic strength.

“…identifying characteristics include high K + selectivity, high single-channel conductance, activation by both cytoplasmic Ca 2+ and depolarizing voltages, and allosteric modulation of Ca 2 § action by cytoplasmic Mg 2+ (Many, 1981;Barrett et al, 1982;Methfessel and Boheim, 1982;Moczydlowski and Latorre, 1983;Magleby and Pallotta, 1983;Petersen and Maruyama, 1984;Blatz and Magleby, 1984;Yellen, 1984;Eisenman et al, 1986;Golowasch et al, 1986; Oberhauser, A., O. Alvarez, and R. Latorre, manuscript submitted for publication). Recently, a high-affinity inhibitor directed against this channel was discovered in the venom of the scorpion Leiurus quinquestriatus (Miller et al, 1985), from which it was subsequently purified (Smith et al, 1986).…”