Activation of Ca21-activated K1 (maxi-K1) channel by angiotensin II in myocytes of the guinea pig ileum

Romero, Fernando, Bagnólia A. Silva, Viviane L. A. Nouailhetas, and Jeannine Aboulafia. Activation of Ca21activated K1 (maxi-K1) channel by angiotensin II in myocytes of the guinea pig ileum. Am. J. Physiol. 274 (Cell Physiol. 43): C983–C991, 1998.—We investigated the regulation of the Ca21-activated K1 (maxi-K1) channel by angiotensin II (ANG II) and its synthetic analog, [Lys2]ANG II, in freshly dispersed intestinal myocytes. We identified a maxi-K1 channel population in the inside-out patch configuration on the basis of its conductance (257 6 4 pS in symmetrical 150 mM KCl solution), voltage and Ca21 dependence of channel opening, low Na1-to-K1 and Cl2-to-K1 permeability ratios, and blockade by external Cs1 and tetraethylammonium chloride. ANG II and [Lys2]ANG II caused an indirect, reversible, Ca21and dose-dependent activation of maxi-K1 channels in cell-attached experiments when cells were bathed in high-K1 solution. This effect was reversibly blocked by DUP-753, being that it is mediated by the AT1 receptor. Evidences that activation of the maxi-K1 channel by ANG II requires a rise in intracellular Ca21 concentration ([Ca]i) as an intermediate step were the shift of the open probability of the channel-membrane potential relationship to less positive membrane potentials and the sustained increase in [Ca]i in fura 2-loaded myocytes. The preservation of the pharmacomechanical coupling of ANG II in these cells provides a good model for the study of transmembrane signaling responses to ANG II and analogs in this tissue.