Insulin-induced improvement of postischemic recovery is abolished by inhibition of protein kinase C in rat heart.
OBJECTIVE
We demonstrated earlier that postischemic addition of insulin improves recovery of function in isolated rat heart by phosphatidylinositol 3-kinase. Activation of phosphatidylinositol 3-kinase before ischemia improves recovery of the heart after ischemia through protein kinase C. We tested whether protein kinase C activation is required for the positive inotropic effect of insulin during reperfusion.


METHODS
Isolated working rat hearts were perfused with Krebs-Henseleit buffer containing [2-(3)H]glucose (5 mmol/L, 0.05 microCi/mL) plus oleate (0.4 mmol/L) and were subjected to 15 minutes of global ischemia followed by 35 minutes of reperfusion with or without insulin (1 mU/mL). We measured cardiac power, glucose uptake, and tissue metabolites. The protein kinase C inhibitor chelerythrine (5 micromol/L) was added either at the beginning of the experiment or together with insulin. Experiments were repeated under normoxic conditions.


RESULTS
Cardiac power before ischemia was 9.63 to 12.4 mW. Insulin improved recovery of power after ischemia (96.3% +/- 10.8% versus 65.7% +/- 3.79%, P <.05). This effect was abolished by chelerythrine (55.3% +/- 6.49%). However, chelerythrine given at reperfusion did not block insulin's effect on recovery (101.0% +/- 4.25%, P <.05). Postischemic glucose uptake was not increased by insulin (3.07 +/- 0.32 before, 3.45 +/- 0.34 micromol/min/gdw after ischemia, not significant) and was not affected by chelerythrine (3.01 +/- 0.26 before, 3.29 +/- 0.32 micromol/min/gdw after ischemia, not significant). Under normoxic conditions, chelerythrine did not influence insulin's effects on glucose uptake or power.


CONCLUSIONS
The results suggest that (1) insulin's effect on recovery is dependent on ischemia-induced protein kinase C activation, (2) the activity of protein kinase C during reperfusion may not be important for this effect of insulin, and (3) protein kinase C plays no role in insulin's effect on glucose uptake under normoxic or postischemic conditions.
Fischer-Rasokat
Ulrich
U
Department of Cardiovascular Surgery, Albert-Ludwigs University of Freiburg, Germany.
Doenst
Torsten
T
D000470:Alkaloids; D000818:Animals; D053119:Benzophenanthridines; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005947:Glucose / Q000378:metabolism; D066298:In Vitro Techniques; D007328:Insulin / Q000494:pharmacology*; D008297:Male; D009200:Myocardial Contraction / Q000187:drug effects*; D015428:Myocardial Reperfusion Injury / Q000201:enzymology / Q000503:physiopathology*; D009206:Myocardium / Q000201:enzymology* / Q000378:metabolism; D010617:Phenanthridines / Q000494:pharmacology; D011493:Protein Kinase C / Q000037:antagonists & inhibitors* / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D013268:Stimulation, Chemical
D000470:Alkaloids; D053119:Benzophenanthridines; D004791:Enzyme Inhibitors; D007328:Insulin; D010617:Phenanthridines; C016299:chelerythrine; D011493:Protein Kinase C; D005947:Glucose