Abstract

We have described previously positive inotropy and increased levels of inositol-l-phosphate as in vitro responses to angiotensin II in cardiac tissue. In this study, changes in cardiac myocyte-free cytosolic calcium stimulated by angiotensin II were monitored with the fluorescent calcium indicator dye Fura-2. There was an initial peak transient increase followed by a sustained increase in cytosolic-free calcium in response to angiotensin II (10(-9)-10(-6) M). The peak transient response in cytosolic-free calcium after addition of angiotensin II (10(-7) M) occurred at 23 +/- 4 sec and was stimulated 2.16-fold (332 +/- 56 nM) above basal levels (154 +/- 14.7 nM). The calcium response was blocked or reversed by addition of verapamil (10(-8) M), lanthanum (0.2 mM) and zero calcium buffer. Angiotensin II receptor-mediated stimulation of inositol phosphates was quantified after separation by high-performance liquid chromatography in cultured chick heart cells prelabeled with L-myo-[1,2-3H(N)]inositol. A time course indicated that the peak response of the angiotensin II (10(-8) M)-stimulated increase in inositol-1,4,5-trisphosphate was at 30 sec. Angiotensin II (10(-8) M) significantly stimulated inositol-1,4-diphosphate (45%) and inositol-1,4,5-trisphosphate (78%) above basal levels. Bordetella pertussis toxin treatment of myocyte cultures in doses (500 ng/ml, 24 hr) shown to fully ADP-ribosylate a toxin-sensitive 41 KD alpha-subunit, blocked completely the angiotensin II-stimulated increases in inositol 1,4-diphosphate, inositol-1,4,5-trisphosphate and inositol 1,3,4,5-tetrakisphosphate. The rise in cytosolic-free calcium in response to angiotensin II was not blocked or inhibited by toxin pretreatment.(ABSTRACT TRUNCATED AT 250 WORDS)