Activation of Ca2+-activated K+(maxi-K+) channel by angiotensin II in myocytes of the guinea pig ileum

Abstract

We investigated the regulation of the Ca²⁺-activated K⁺(maxi-K⁺) channel by angiotensin II (ANG II) and its synthetic analog, [Lys²]ANG II, in freshly dispersed intestinal myocytes. We identified a maxi-K⁺channel population in the inside-out patch configuration on the basis of its conductance (257 ± 4 pS in symmetrical 150 mM KCl solution), voltage and Ca²⁺dependence of channel opening, low Na⁺-to-K⁺and Cl⁻-to-K⁺permeability ratios, and blockade by external Cs⁺and tetraethylammonium chloride. ANG II and [Lys²]ANG II caused an indirect, reversible, Ca²⁺- and dose-dependent activation of maxi-K⁺channels in cell-attached experiments when cells were bathed in high-K⁺solution. This effect was reversibly blocked by DUP-753, being that it is mediated by the AT₁receptor. Evidences that activation of the maxi-K⁺channel by ANG II requires a rise in intracellular Ca²⁺concentration ([Ca²⁺]_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 [Ca²⁺]_iin 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.