ALPHA-ADRENERGIC PRESERVATION OF MYOCARDIAL PH DURING ISCHEMIA IS PKCISOFORM DEPENDENT

alpha-adrenergic stimulation of patients with ischemic heart disease s hould intuitively impose a destructive stress. However, therapeutic al pha(1)-adrenergic receptor mediated cardioadaptation prior to myocardi al ischemia protects ventricular mechanical function, promotes electro physiologic stability, and preserves myocyte viability. Prior to an an ticipated cardiac ischemic insult, alpha(1)-adrenergic preconditioning attenuates ischemic myocardial acidosis by a protein kinase C-(PKC) d ependent mechanism. The alpha(1)-adrenoceptor can directly stimulate c alcium-independent nPKC isoforms via diacylglycerol (DAG) or indirectl y stimulate calcium-dependent cPKC isoforms through the release of int racellular calcium via inositol triphosphate, (IP3). We hypothesized t hat alpha(1)-adrenergic limitation of ischemic acidosis is mediated by the family of calcium-dependent PKC isoforms. [P-31]NMR spectra were obtained in isolated, buffer perfused rat hearts treated with alpha(1) -adrenergic stimulation [phenylephrine (PE) 50 mu M, 2 min]; PKC block ade [chelerythrine chloride, (Chel) 20 mu M]; or stearoyl-arachidonoyl glycerol (SAG, a DAG analogue, 100 mu M, 2 min) administered 10 min p rior to ischemia. Control hearts were perfused under normoxic conditio ns for 20 min. All hearts were then subjected to global ischemia (20 m in, 37.5 degrees C), Developed pressure (DP) and heart rate were recor ded continuously. pH(i) was obtained from chemical shift of inorganic phosphate. Immunohistochemical staining was utilized to delineate the translocation and activation profiles of specific PRC profiles establi shed with each stimulus. Pre-ischemic alpha(1)-adrenergic stimulation did attenuate the myocellular hydrogen ion accumulation during sustain ed normothermic ischemia (6.90 +/- 0.13 vs control 6.54 +/- 0.10; P < 0.05). General PKC inhibition abrogated this effect (end-ischemic pH 6 .17 +/- 0.10; P < 0.05 vs control and PE). Ischemic acidosis was not a ttenuated following selective nPKC stimulation (SAG, 6.48 +/- 0.08; NS vs control). Myocellular immuno-histochemical staining revealed trans location of the calcium-independent PKC-epsilon isoform in the calcium -dependent PKC (SAG) group, but not in response to alpha(1)-adrenergic stimulation. The results suggest that (1) alpha(1)-adrenoceptor stimu lation Limits ischemic acidosis, (2) alpha(1)-adrenergic stimulated at tenuation of ischemic acidosis is PRC dependent, (3) direct nPKC stimu lation with SAG does not Limit ischemic acidosis, and (4) SAG stimulat es nPKC-epsilon isoform activation where alpha(1)-adrenergic stimulati on does not. We conclude that alpha(1)-adrenergic stimulation limits i schemic acidosis by a cPKC-dependent mechanism and that the mobilizati on of the IP3 arm by receptor stimuli suppresses PKC-epsilon thus perm itting the limitation of ischemic acidosis. (C) 1996 Academic Press, I nc.