Stimulation of phosphatidylinositol metabolism in the heart

Receptor-stimulated hydrolysis of inositol phospholipids was studied in atrial and ventricular myocytes isolated from guinea-pigs. Acetylcholine and carbachol stimulated inositol phosphate accumulation with a maximum of more than 12 times the unstimulated values in atrial myocytes and 7 times in ventricular myocytes. The vasoactive peptides angiotensin II and vasopressin also stimulated inositol phosphate accumulation, but the maximum effect was lower than that mediated through muscarinic receptors. However, the adenosine analogues, L-N6-phenylisopropyladenosine and 5'N-ethylcarboxamidoadenosine which, like muscarinic agonists depress cardiac contractility, did not affect inositol phosphate accumulation at concentrations up to 10(-4) mol/l. Stimulation of phosphatidylinositol turnover in heart bears no obvious relationship to either contractility or release of atrial natriuretic factor.