Characterization of the high-conductance Ca2+-activated K+ channel in adult human skeletal muscle

Abstract

Ca(2+)-activated K+ channels of a large conductance (BKCa) in human skeletal muscle were studied by patch clamping membrane blebs and by using the three microelectrode voltage-clamp recording technique on resealed fibre segments. Single-channel recordings in bleb-attached and inside-out modes revealed BKCa conductances of 230 pS for symmetrical and 130 pS for physiological K+ distributions. Open probability increased with membrane depolarization and increasing internal [Ca2+]. The Hill coefficient was 2.0, indicating that at least two Ca2+ ions are required for full activation. Kinetic analysis revealed at least two open and three closed states. An additional long-lived inactivated state, lasting about 0.5-20 s, was observed following large depolarizations, when extracellular K+ was lowered to physiological values. BKCa were blocked by three means: (1) externally by tetraethylammonium which reduced single-channel amplitude (IC50 approx. 0.3 mM); (2) internally by polymyxin B which decreased the open probability (IC50 approx. 5 micrograms/ml); and (3) externally by charybdotoxin which caused long-lasting periods of inactivation (IC50 < 10 nM). Measurements on resealed fibre segments at physiological [K+] were in accordance with the single-channel data: only when intracellular [Ca2+] was elevated did charybdotoxin (50 nM) reduce the macroscopic membrane K+ conductance with depolarizing voltage steps.

BK Channels in Human Glioma Cells

“…Our data suggest that the whole cell BK conductance would be increased approximately twofold under these conditions. BK current enhancement by elevated [K ϩ ] o is due in part to an increased singlechannel conductance, in line with other studies (Hurley et al 1999;Lerche et al 1995;Wann and Richards 1994). This may be a result of allosteric actions of K ϩ ions themselves on the channel or altered permeation properties with high [K ϩ ] o .…”

“…Consistent with previous studies (Hurley et al 1999;Lerche et al 1995;Wann and Richards 1994), the unitary current was increased by elevating [K ϩ ] o . Figure 9D illustrates the effect of increasing [K ϩ ] o on unitary current amplitude in a representative outside-out patch.…”

Membrane Electrical Activity Elicits Inositol 1,4,5-Trisphosphate-dependent Slow Ca2+ Signals through a Gβγ/Phosphatidylinositol 3-Kinase γ Pathway in Skeletal Myotubes

“…1F, cells accelerate the repolarization rate reaching 15-ms action potential duration at 45 Hz, allowing one action potential for each pulse of the train. This rate increase may be explained by enhanced chloride and potassium conductances activated by the calcium increase (26,27) during the electrical stimulation shown in Fig. 1B.…”

Contribution of a non‐inactivating potassium current to the resting membrane potential of fusion‐competent human myoblasts.

“…'K(no) however, is distinct from IBK(Ca) as 'K(no) was present when the intracellular Ca2P concentration was greatly reduced and it is insensitive to charybdotoxin. In addition, the single-channel conductance of 'K(ni) is 10-fold less than that Of IBK(ca) channels measured in adult human skeletal muscle (Lerche et al 1995). IK(ni) is also distinct from another calcium-activated potassium channel, ISK(Ca), as the activity of this channel is insensitive to voltage (Blatz & Magleby, 1986).…”