[Effects of angiotensin II on spontaneous cytosolic calcium releases in ventricular myocytes of adult normal and hypertensive rats].

This study investigated the effects of angiotensin II (Ang II) (10(-9)M to 10(-7)M) on calcium releases in ventricular myocytes from normal and renal hypertensive adult rats (Goldblatt 2K-1C). Newly, isolated myocytes were loaded with fluorescent indo-1/AM and studied at rest or under electrical stimulation. The variation of the ratio of indo-1 emission (405 nm/480 nm) was taken as a measure of cytosolic calcium variations. Five parameters were investigated from each peak systolic indo-1 ratio before and after Ang II addition: amplitude variation, duration with analysis of a rise time and a fall time, and frequency of spontaneous calcium releases. Following changes were observed: in unstimulated myocytes exhibiting spontaneous contractile activity, increase in frequency of calcium transients, at 10(-7)M, in normal cells (+ 157 +/- 27%; p < 0.01) and whatever Ang II concentration in hypertrophied cells (+ 79 +/- 31%; p < 0.01; + 82 +/- 25%, p < 0.01; + 285 +/- 50%, p < 0.01 à 10(-9)M, 10(-8)M, 10(-7)M); in stimulated myocytes, prolongation of the duration of calcium transients explained by the occurrence of calcium releases during fall time. In addition, 50% of myocytes exhibited spontaneous releases of calcium in the interstimulus interval. Increase in calcium transients duration was statistically significant, whatever Ang II concentration in hypertrophied cells (+ 36 +/- 20%, p < 0.05; + 39 +/- 18%, p < 0.01; + 77 +/- 34%, p < 0.01 à 10(-9)M, 10(-8)M, 10(-7)M) and only at 10(-7)M in normal cells (+ 68 +/- 22% p < 0.01). Similar results were observed in fall time.(ABSTRACT TRUNCATED AT 250 WORDS)