Abstract
To examine the role of cyclic ADP-ribose (cADP-ribose) as a second messenger downstream of angiotensin II (Ang II) receptor activation in the heart, ADP-ribosyl cyclase activity was measured in a crude membrane fraction of ventricular myocytes. Ang II at 10–100nM increased ADP-ribosyl cyclase activity by 40–90% in the ventricular muscle of neonatal (2–4-day-old) rats, but not in fetal or adult hearts. This increase was inhibited by the Ang II antipeptide. Stimulation of ADP-ribosyl cyclase was reproduced by GTP and guanosine 5´-[γ-thio]triphosphate, and prevented by guanosine 5´-[β-thio]diphosphate. Prior treatment of the rats with cholera toxin A and B subunits also blocked the Ang II-induced activation. The density of Ang II receptors detected as [3H]Ang II binding was higher in neonatal than adult rats. These results demonstrate the existence of a signalling pathway from Ang II receptors to membrane-bound ADP-ribosyl cyclase in the ventricular muscle cell and suggest that the Ang II-induced increase in cADP-ribose synthesis is involved in the regulation of cardiac function and development.
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