α-adrenergic preservation of myocardial pH during ischemia is PKC isoform dependent

α-adrenergic stimulation of patients with ischemic heart disease should intuitively impose a destructive stress. However, therapeutic α-adrenergic receptor mediated cardioadaptation prior to myocardial ischemia protects ventricular mechanical function, promotes electrophysiologic stability, and preserves myocyte viability. Prior to an anticipated cardiac ischemic insult, α₁-adrenergic preconditioning attenuates ischemic myocardial acidosis by a protein kinase C-(PKC) dependent mechanism. The α₁-adrenoceptor can directly stimulate calcium-independent nPKC isoforms via diacylglycerol (DAG) or indirectly stimulate calcium-dependent cPKC isoforms through the release of intracellular calcium via inositol triphosphate, (IP3). We hypothesized that α₁-adrenergic limitation of ischemic acidosis is mediated by the family of calcium-dependent PKC isoforms. [³¹P]NMR spectra were obtained in isolated, buffer perfused rat hearts treated with α₁-adrenergic stimulation [phenylephrine (PE) 50 μM, 2 min]; PKC blockade [chelerythrine chloride, (Chel) 20 μM]; or stearoyl-arachidonoyl glycerol (SAG, a DAG analogue, 100 μM, 2 min) administered 10 min prior to ischemia. Control hearts were perfused under normoxic conditions for 20 min. All hearts were then subjected to global ischemia (20 min, 37.5°C). Developed pressure (DP) and heart rate were recorded continuously. pH(i) was obtained from chemical shift of inorganic phosphate. Immunohistochemical staining was utilized to delineate the translocation and activation profiles of specific PKC profiles established with each stimulus. Pre-ischemic α₁-adrenergic stimulation did attenuate the myocellular hydrogen ion accumulation during sustained 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 attenuated following selective nPKC stimulation (SAG, 6.48 ± 0.08; NS vs control). Myocellular immunohistochemical staining revealed translocation of the calcium- independent PKC-ε isoform in the calcium-dependent PKC (SAG) group, but not in response to α₁-adrenergic stimulation. The results suggest that (1) α₁-adrenoceptor stimulation limits ischemic acidosis, (2) α₁-adrenergic stimulated attenuation of ischemic acidosis is PKC dependent, (3) direct nPKC stimulation with SAG does not limit ischemic acidosis, and (4) SAG stimulates nPKC-ε isoform activation where α₁-adrenergic stimulation does not. We conclude that α₁-adrenergic stimulation limits ischemic acidosis by a cPKC- dependent mechanism and that the mobilization of the IP3 arm by receptor stimuli suppresses PKC-ε, thus permitting the limitation of ischemic acidosis.