Betaine generation in cardiac myocytes after adrenergic activation of phosphatidylcholine hydrolysis.
In this report, effects of alpha 1-adrenergic stimulation on phosphatidylcholine (PC) hydrolysis and the subsequent generation of water-soluble choline metabolites were investigated after preincubation of isolated cardiac myocytes of adult rats with [methyl-3H]choline. Choline uptake into cardiac myocytes was apparently mediated by a choline carrier which could be inhibited by hemicholinium-3. Analysis of the intracellular choline metabolites was performed by HPLC. Adrenergic stimulation of cardiac myocytes by (-)-phenylephrine, which is also known to activate the phosphoinositide signaling system, induced the generation of betaine as a selective signal transduction response. Agonist-induced generation of betaine in cardiac myocytes was maximal at 10 min after stimulation, and was optimal at physiologically relevant (-)-phenylephrine concentrations (1-10 microM). Betaine accumulation was transient, and no betaine remained detectable after 15 min. CDP-choline, however, was still elevated after 15 min which is indicative of continued PC resynthesis after adrenergic stimulation. The source of betaine in cellular signalling appeared to be hydrolysis of membrane PC to phosphatidic acid and choline by phospholipase D with subsequent oxidation of choline to betaine. This is based on the observation that radioactivity in unstimulated cells is present only in the lipid phase (presumably as PC) or as phosphocholine in the aqueous phase of the cells. The latter finding suggests that choline is rapidly phosphorylated after uptake into cardiac myocytes. Collectively, these results suggest a hypothetical role of betaine in the cellular signal transduction response to alpha 1-adrenergic stimulation in cardiac myocytes.
Meister
A
A
Department of Biochemistry and Molecular Biology, University of Hamburg, Germany.
Kleuser
B P
BP
Ollert
M W
MW
Gercken
G
G
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000818:Animals; D001622:Betaine / Q000378:metabolism*; D002478:Cells, Cultured; D006868:Hydrolysis; D009206:Myocardium / Q000378:metabolism*; D010656:Phenylephrine / Q000494:pharmacology*; D010713:Phosphatidylcholines / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D011942:Receptors, Adrenergic, alpha / Q000378:metabolism*; D015398:Signal Transduction
D000316:Adrenergic alpha-Agonists; D010713:Phosphatidylcholines; D011942:Receptors, Adrenergic, alpha; D010656:Phenylephrine; D001622:Betaine