Phosphorylation of myosin in perfused rabbit and rat hearts.
Working perfused rabbit and rat hearts were used to determine whether changes in myosin P-light chain phosphate content could affect cardiac contractility. Control perfused rabbit and rat hearts contained 0.48 +/- 0.02 and 0.61 +/- 0.02 mol phosphate/mol P-light chain, respectively. Perfusion of 1) rabbit hearts with 0.1 microM isoproterenol for 30 s, 2) rabbit or rat hearts with a fivefold increase in perfusate [Ca2+] for 30 s, or 3) rabbit hearts with a threefold increase in [Ca2+] for 5 and 15 min caused significant increases in LV dP/dtmax, but had no effect on P-light chain phosphate content. Perfusion of rabbit hearts with Ca2+-free buffer or buffer containing 22 mM K+ caused complete cessation of contractile activity within 30 s and reduced P-light chain phosphate content to 50 and 70%, respectively, of control values after 30 min. Reperfusion of hearts exposed to 22 mM K+ with control buffer restored LV dP/dtmax to control values within 10 min, whereas P-light chain phosphate content remained at 70% of control value. Thus, changes in cardiac contractile state were not accompanied by changes in the extent of phosphorylation of P-light chain.
D000818:Animals; D002118:Calcium / Q000378:metabolism; D005260:Female; D007545:Isoproterenol / Q000494:pharmacology; D008297:Male; D009200:Myocardial Contraction / Q000187:drug effects; D009206:Myocardium / Q000201:enzymology*; D009218:Myosins / Q000378:metabolism*; D010477:Perfusion; D010710:Phosphates / Q000378:metabolism; D010762:Phosphorylase a / Q000378:metabolism; D010766:Phosphorylation; D011188:Potassium / Q000494:pharmacology; D011817:Rabbits
D010710:Phosphates; D010762:Phosphorylase a; D009218:Myosins; D007545:Isoproterenol; D011188:Potassium; D002118:Calcium