Depressed [Ca2+]i responses to isoproterenol and cAMP in isolated cardiomyocytes from experimental diabetic rats.
Experimentally, diabetic rat hearts are characterized by diminished responses to beta-adrenergic stimulation. Among the aberrant responses are diminished beta-adrenoceptor number and depressed contractile protein activity. In this study, intracellular Ca2+ concentration ([Ca2+]i) was determined by microfluorescence in response to beta-adrenergic stimulation to understand the basis for the changes in the beta-adrenergic pathway in diabetic myocardium. In quiescent myocytes, isoproterenol caused a decrease in [Ca2+]i, which was blocked by timolol and thapsigargin. This suggests that the beta-agonist-induced [Ca2+]i changes are mediated, in part, by sarcoplasmic reticulum Ca-adenosinetriphosphatase. Diabetic myocytes showed a blunted response to isoproterenol, which was reversed by insulin treatment. In electrically stimulated myocytes, isoproterenol and 8-bromo-adenosine 3',5'-cyclic monophosphate (cAMP) increased [Ca2+]i and contraction in a concentration-dependent manner. Electrically stimulated diabetic myocytes demonstrated a depressed maximum [Ca2+]i response to isoproterenol and 8-bromo-cAMP without a change in sensitivity. These data suggest that in addition to alterations in beta-adrenoceptor function there are postreceptor defects in diabetic myocardium that may impair the regulation of [Ca2+]i in diabetic myocardium.
Yu
Z
Z
Faculties of Pharmaceutical Sciences, University of British Columbia, Vancouver, Canada.
Quamme
G A
GA
McNeill
J H
JH
D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D000242:Cyclic AMP / Q000494:pharmacology*; D003921:Diabetes Mellitus, Experimental / Q000378:metabolism* / Q000473:pathology; D004558:Electric Stimulation; D007328:Insulin / Q000494:pharmacology; D007425:Intracellular Membranes / Q000378:metabolism*; D007545:Isoproterenol / Q000494:pharmacology*; D008297:Male; D009206:Myocardium / Q000378:metabolism* / Q000473:pathology; D009994:Osmolar Concentration; D051381:Rats; D017208:Rats, Wistar; D012016:Reference Values
D007328:Insulin; D015124:8-Bromo Cyclic Adenosine Monophosphate; D000242:Cyclic AMP; D007545:Isoproterenol; D002118:Calcium