Calmodulin antagonists do note inhibit IKCa channels of human erythrocytes

Patch-clamp recordings were performed to study the effects of three calmodulin (CaM) antagonists on the gating of intermediate calcium-activated K+ channels (IKCa) of human erythrocytes In the cell-attached configuration, both opening frequency and open probability of IKCa channels were not significantly different in control cells and in those incubated with calmidazolium, trifluoperazine or W7. IKCa channels in excised membrane patches, were normally activated by the calcium bathing the cytoplasmic side in the presence of CaM antagonists, at calcium concentrations ranging from 10(-7) to 10(-3) M. The activity of IKCa channels, which had been previously up-modulated by an endogenous cAMP-dependent protein kinase, was not inhibited when perfused with CaM antagonists. The results presented in this study demonstrate that calmodulin antagonists do not inhibit the activity of native IKCa channels of human erythrocytes. These data are in accordance with findings on the cloned IKCa indicating that calmodulin is constitutively associated with these channels. (C) 2002 Elsevier Science B.V. All rights reserved.