Activation of Ca(2+)-activated K+ (maxi-K+) channel by angiotensin II in myocytes of the guinea pig ileum.
We investigated the regulation of the Ca(2+)-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, Ca(2+)- 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 AT1 receptor. 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+]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.
Romero
F
F
Department of Biophysics, Universidade Federal de São Paulo, Escola Paulista de Medicina, Brazil.
Silva
B A
BA
Nouailhetas
V L
VL
Aboulafia
J
J
D000804:Angiotensin II / Q000031:analogs & derivatives / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000502:physiology*; D005260:Female; D006168:Guinea Pigs; D007082:Ileum / Q000166:cytology / Q000378:metabolism*; D008297:Male; D009130:Muscle, Smooth / Q000166:cytology / Q000378:metabolism; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000187:drug effects* / Q000502:physiology*
D015221:Potassium Channels; D000804:Angiotensin II; C058393:angiotensin II, Lys(2)-; D002118:Calcium