Hormonally specific expression of cardiac protein kinase activity

Abstract

The relationship between the effects of isoproterenol and prostaglandin El (PGE1) on contractile state, cyclic AMP accumulation, and the activation states of protein kinase (ATP: protein phosphotransferase, EC 2.7.1.37), phosphorylase kinase, glycogen synthase, and glycogen phosphorylase have been studied in the isolated perfused rat heart. Perfusion of hearts with isoproterenol (10 or 80 nM) caused enhancement of left ventricular dP/dt (P, pressure), increased intracellular cyclic AMP, increased the activation states of protein kinase, phosphorylase kinase, glycogen phosphorylase, and conversion of glycogen synthase to a less active form. PGE1 (2 or 30 ;&M) increased cyclic AMP accumulation and activated protein kinase, but caused no detectable changes in dP/dt or the activation states of the protein kinase substrates involved in glycogen metabolism. Perfusion of hearts with either 10 nM isoproterenol or 30 1sM PGE1 produced comparable increases in cyclic AMP accumulation and protein kinase activity. Exposure of hearts to a combination of these agents caused additive effects on cyclic AMP content and protein kinase activity. However, values for phosphorylase kinase, glycogen phosphorylase, glycogen synthase, and dP/dt did not differ from those observed in the presence of 10 nM isoproterenol alone. The failure of PGE1 to stimulate phosphorylation of protein kinase substrates was not due to an increase in phosphorylase phosphatase activity. We conclude that an increase in intracellular cyclic AMP and the subsequent activation of protein kinase are insufficient to change either the activities of phosphorylase kinase, glycogen phosphorylase, and glycogen synthase or the inotropic state of eart muscle. Kuo and Greengard (1) have advanced the idea that ubiquitous cyclic AMP-dependent protein kinases (ATP:protein phosphotransferase, EC 2.7.1.37) mediate most, if not all, of the effects of cAMP in eukaryotes (1-3). According to this hypothesis the ability of a hormone to elicit a response mediated by cAMP would be determined by the presence of the appropriate adenylate cyclase-linked receptor on the surface of the cell and by the presence within the cell of appropriate substrates for protein kinase. Thus, receptors specify the spectrum of hormonal sensitivity of a cell and available substrates specify the precise response. Much evidence supports the universality of Kuo and Greengard's hypothesis. It is apparent that cAMP is the only ligand necessary for the activation of protein kinase (4, 5). Numerous events, notably glycogenolysis (2) and lipolysis (6), result from phosphorylation of proteins by cAMP-dependent protein kinases subsequent to elevation of intracellular cAMP. Other than phosphodiesterase, the regulatory subunit of protein kinase appears to be the major high-affinity binding protein for cAMP (1). As noted by Rall, however, the protein kinase hypothesis presents us with "the unsatisfying picture of the catalytic subunit of protein kinase swimming about, happily phosphorylating a variety of cellula...

Compartmentation of Cyclic Nucleotide Signaling in the Heart

“…120 -122 Important differences were observed when comparing hearts perfused with different agonists activating the cAMP cascade, particularly via ␤ 1 -AR and prostaglandin E 1 receptor (PGE 1 -R): with isoproterenol (ISO), cAMP is elevated, the force of contraction is enhanced, soluble and particulate PKA are activated, and the activity of phosphorylase kinase and glycogen phosphorylase is increased; with PGE 1 , cAMP content and soluble PKA activity are also increased, but there is no change in contractile activity or in the activities of PKA substrates that regulate glycogen metabolism. 122,123 Similar results were reproduced in isolated myocytes. 124 The situation is even more complex if one considers that a given cardiac myocyte expresses many other G s -coupled receptors, besides ␤ 1 -ARs and PGE 1 -Rs, that increase cAMP but produce different effects.…”

Different Compartmentation of Responses to Brain Natriuretic Peptide and C-Type Natriuretic Peptide in Failing Rat Ventricle

“…This study and other studies with ANP and CNP (Pierkes et al, 2002;Frantz et al, 2013) support our present results that BNP and CNP signal in different functional compartments. The discrepancy between BNP and CNP on NIR and LR, despite both increasing cGMP, is analogous to findings in the cAMP pathway, where PGE1 and isoprenaline both increased cAMP, but only isoprenaline showed contractile effects (Kaumann and Birnbaumer, 1974;Hayes et al, 1979). The reason for the differential functional compartmentation by BNP and CNP could be different localization of the receptors on the cell membrane combined with restricted diffusion of cGMP.…”

Soluble Adenylyl Cyclase Reveals the Significance of cAMP Compartmentation on Pulmonary Microvascular Endothelial Cell Barrier

“…However, as studies advanced, it became unclear how different external stimuli, which similarly elevate cAMP, selectively control different physiological processes. 1,2 These and related studies have given rise to the evolving hypothesis that cAMP signaling occurs within spatially and temporally confined microdomains. [2][3][4][5] Whole cell cAMP concentration is established by the activities of ACs that synthesize cAMP and phosphodiesterases that hydrolyze it.…”