Excitation-contraction coupling in ventricular myocytes: effects of angiotensin II.
The effects of the vasoactive peptide angiotensin II (AII) on contractility and excitation-contraction coupling in isolated adult rabbit ventricular myocytes were investigated. In most ventricular myocytes, AII (10(-8) M) induced a significant increase in fractional shortening which was not associated with an increase in the calcium transient measured with indo-1. AII did increase the intracellular pH by approximately 0.2 5 pH units coincident with the positive inotropic effect. Effects of AII on pH and contractility were blocked by inhibitors of Na+/H+ exchange. AII also increased the rate of pHi recovery from intracellular acidosis at pHi values above 6.9. AII was shown not to affect the L-type inward calcium current. However, in an occasional cell, AII was observed to cause a slight increase in the calcium transient. We hypothesize that this response may reflect an increase of calcium influx on the sodium calcium exchanger, as a consequence of an increase in subsarcolemmal sodium concentration resulting from enhanced Na(+)-H+ exchange.
Barry
W H
WH
Division of Cardiology, University of Utah Medical School, Salt Lake City 84132, USA.
Matsui
H
H
Bridge
J H
JH
Spitzer
K W
KW
D000804:Angiotensin II / Q000494:pharmacology*; D000818:Animals; D002478:Cells, Cultured; D004594:Electrophysiology; D006168:Guinea Pigs; D006863:Hydrogen-Ion Concentration; D009200:Myocardial Contraction / Q000187:drug effects*; D011817:Rabbits; D014662:Vasoconstrictor Agents / Q000494:pharmacology*; D016276:Ventricular Function
D014662:Vasoconstrictor Agents; D000804:Angiotensin II