Differential Ca2+ sensitivities of BK(Ca) isochannels in bovine mesenteric vascular smooth muscle

S. C. Sansom, James D Stockand

Research output: Contribution to journalArticlepeer-review


The planar bilayer method was used to characterize the properties of large Ca2+-activated K+ [BK(Ca)] channels of smooth muscle from bovine mesenteric arteries. We found two isochannels of BK(Ca), differing in sensitivity to Ca2+ on the intracellular side of the channel. The first isochannel, K(c1), had a single-channel conductance of 287 ± 8 pS and required a potential of -33 mV to activate to an open probability (P(o)) of 0.5 with 1 μM Ca2+. The single-channel conductance of the second isochannel, K(c2) (282 ± 8 pS), was not statistically different from that of K(c1) but required a potential of 41 mV to activate to a P(o) of 0.5 with 1.0 μM Ca2+. At a channel voltage of 0 mV, the Ca2+ concentrations for activating P(o) to 0.5 were 0.2 and 10 μM for K(c1) and K(c2), respectively. The equivalent gating charges, estimated from the Boltzmann equation, were 2.4 and 2.2 for K(c1) and K(c2), respectively. The K/Cl selectivity of K(c1) was >40 and not significantly different from K(c2). The P(o) of either isochannel did not change when protein kinase A or alkaline phosphatase was added to the intracellular side. We conclude that bovine mesenteric arteries contain two distinct isochannels of BK(Ca) that differ in Ca2+ sensitivity but are identical with respect to single-channel conductance, equivalent gating charge, and K-/Cl- selectivities.

Original languageEnglish (US)
JournalAmerican Journal of Physiology - Cell Physiology
Issue number5 35-5
StatePublished - 1994
Externally publishedYes


  • gating charge
  • planar bilayers
  • potassium channels

ASJC Scopus subject areas

  • Clinical Biochemistry
  • Cell Biology
  • Physiology


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