Activation of calcium-sensitive potassium channels in L6 skeletal myocytes by arginine vasopressin requires extracellular calcium

The effects of extracellular application of arginine vasopressin (AVP) upon membrane currents in L6 skeletal myocytes was investigated using the whole-cell configuration of the patch-clamp technique. At O mV AVP produced large amplitude, transient outward currents that reversed when the clamping potential was changed to -100 mV (negative to E_K) The effects of alterations in the extracellular K⁺ concentration upon the current reversal potential suggested that the current elicited by AVP was carried mainly by K⁺ ions. Intracellular dialysis with 10 μM inositol 1,4,5-trisphosphate (InsP₃) elicited similar currents but only in 6/14 cells. Inclusion of 5 mg ml^-1 heparin in the intracellular solutions was ineffective at inhibiting the current responses to AVP. The AVP-induced current was totally abolished when the intracellular EGTA concentration was increased from 0.05 mM to 10 mM or Ca²⁺ was removed from the extracellular perfusing solution. These results suggest that AVP produces activation of a Ca²⁺-sensitive K⁺ conductance in L6 skeletal myocytes by a process dependent upon extracellular Ca²⁺ and not intracellular Ca²⁺ release. © 1995 Academic Press. All rights reserved.