Changes in phosphoinositide turnover in isolated guinea pig hearts stimulated with isoproterenol.

Abstract

The incorporation of 32 P, into phospholamban, troponin I, phosphatidylinositols, and inositol trisphosphates was studied in Langendorff-perfused guinea pig hearts stimulated with isoproterenol. Hearts were perfused with Krebs-Henseleit buffer containing [ 32 P]P| and freezeclamped at different times during the positive inotropic response. Exposure of the hearts to 0.1 /AM isoproterenol for up to 1 minute was associated with significant (up to threefold) increases in phospholamban and troponin I phosphorylation, but there was no significant increase in 32 P incorporation into phospholipids. However, longer exposure (2 minutes or more) to isoproterenol was associated with increases in the degree of P labeling of phosphatidylinositols and phosphatidic acid. Examination of 32 P labeling of Inositol trisphosphates in the same hearts revealed that the radioactivity associated with these compounds decreased with time. The decreases were significant at times of exposure of 2 minutes or longer to 0-adrenergic stimulation. The tissue levels of the inositol 1,4,5-trisphosphate isoform were also measured in hearts perfused with isoproterenol for 3 minutes, and they were found to be significantly lower compared with values obtained in control hearts. The effects of isoproterenol on 32 P incorporation into phospholipids and proteins were observed in the presence of prazosin, and they were completely abolished by the /3-receptor blocker propranolol. Examination of the phosphoinositldespecific phosphoUpase C activity in the perfused hearts revealed that isoproterenol stimulation was associated with a decrease in the membrane-associated enzymatic activity at physiological calcium concentrations. These findings indicate that 0-adrenergic stimulation of isolated hearts is associated with changes in basal phosphatidylinositol turnover that may be mediated, at least in part, by inhibition of the phosphoUpase C enzymatic activity specific for phosphatidylinositols. Received December 28, 1988; accepted April 25, 1989. myofibrils, the sites of phosphorylation are troponin I and C protein, 1 -2 and the increased phosphate incorporation into these proteins is associated with a decrease in the Ca 2+ sensitivity of the myofibrillar Mg 2+ -dependent ATPase activity. 1 ' 3 The site of phosphorylation in SR, due to ^-agonist stimulation, has been shown to be on phospholamban, and stimulation of phosphate incorporation results in increased rates of calcium transport by the SR.1 -4 Dephosphorylation of phospholamban occurs on reversal of the mechanical effects of isoproterenol, 2 and this is probably mediated by protein phosphatases associated with cardiac SR membranes.5 /3-Adrenergic stimulation has also been shown to result in phosphorylation of a 15 kDa protein in sarcolemma, which may be involved in increasing transsarcolemmal calcium flux through the slow inward Ca 2+ channels.6 -7 The activation of glycogenolysis and inactivation of grycogen synthesis are also synchronously controlled by cAMP-dependent phosphorylation 8 to cover energ...

Effect of Concomitant β‐Adrenoceptor Stimulation on α1‐Adrenoceptor‐Mediated Increase of Inositol‐1, 4, 5‐trisphosphate Mass in Adult Rat Cardiomyocytes

“…We could not detect any influence of P-adrenoceptor stimulation on the IP3 mass level in isolated cardiomyocytes. In contrast, decreased incorporation of radiolabelled phosphate into IP3, as well as decreased IP3 mass, was observed after P-adrenoceptor stimulation of isolated perfused guinea pig hearts (Edes et al 1989). Recent studies have indicated that phosphatidylinositol turnover is different in intact heart tissue and in isolated cardiomyocytes (Woodcock et al Anderson et al 1995;Woodcock et al 1995).…”

Isoproterenol Promotes Rapid Ryanodine Receptor Movement to Bridging Integrator 1 (BIN1)–Organized Dyads

“…It remains unidentified how BIN1 rapidly accumulates at t-tubules to generate microdomains within 5 minutes of ISO stimulation. Interestingly, BIN1 is a membrane scaffolding protein with binding affinity to plasma membrane phospholipids 34 , which is known to be altered by acute β-AR stimulation in as short as 1–3 minutes 35 . The potential role of cardiac t-tubule membrane lipid species in BIN1-microdomain formation awaits future studies.…”

Cardiac hypertrophy. Mechanical, neural, and endocrine dependence.

“…In regard to the possibility that protein kinase C may participate in the signal transduction pathway from the 3-receptor, it has recently been reported that f3-adrenergic stimulation of isolated, perfused hearts was associated with changes in basal phosphatidylinositol turnover that may be partially mediated by inhibition of the enzymatic activity of phospholipase C. 78 Stimulation of 83-adrenoceptors by isoproterenol resulted in increased labeling of phosphatidylinositols as well as a decline in the contents and radioactivity of water-soluble inositol triphosphates, including Ins-1,4,5-1P3, in perfused guinea pig hearts. These changes in phosphatidylinositol turnover were blocked by the 13-receptor antagonist propranolol.…”