title: Cardiac myofibrillar phosphorylation and adenosine triphosphatase activity.
abstract: When myofibrils from rat hearts were dissolved in concentrated salt solutions and reprecipitated by dilution, they contained both protein kinase (partly cyclic 3':5'-AMP-dependent) and protein phosphatase activities. Troponin-I was the major protein to be phosphorylated by the endogenous myofibril-associated kinase and by added protein kinase. Approximately 1 mole of phosphate per mole of troponin-I was incorporated from radioactive ATP, but the extent of troponin-I phosphorylation could be varied experimentally. An inverse correlation was found between protein phosphorylation and the maximum Ca2+-stimulated myofibrillar Mg2+-ATPase activity, while the amout of calcium required for half-maximum activation was proportional to the extent of protein phosphorylation. The changes in Mg2+-ATPase activity produced in vitro by protein phosphorylation were reproduced in isolated perfused rat hearts treated for short periods with L-noradrenaline (10(-6)M). The changes in myofibrillar function brought about as the result of the phosphorlyation by cAMP-dependent protein kinase suggest that the contractile response is desensitized in order to cope with the rise in intracellular Ca2+ which results from the action of catecholamines on cardiac ventricular cells.
mesh_terms: D000251:Adenosine Triphosphatases / Q000502:physiology*; D000818:Animals; D002118:Calcium; D000242:Cyclic AMP / Q000378:metabolism; D005260:Female; D008297:Male; D009206:Myocardium / Q000201:enzymology*; D009210:Myofibrils / Q000201:enzymology* / Q000378:metabolism; D009638:Norepinephrine / Q000378:metabolism; D010749:Phosphoprotein Phosphatases / Q000378:metabolism; D010766:Phosphorylation; D010770:Phosphotransferases / Q000378:metabolism*; D011494:Protein Kinases / Q000378:metabolism*; D051381:Rats; D012969:Sodium Fluoride / Q000494:pharmacology; D013268:Stimulation, Chemical
chemical_list: D012969:Sodium Fluoride; D000242:Cyclic AMP; D010770:Phosphotransferases; D011494:Protein Kinases; D010749:Phosphoprotein Phosphatases; D000251:Adenosine Triphosphatases; D002118:Calcium; D009638:Norepinephrine