J Mol Cell Cardiol 30, 2423–2435 (1998) Article No. mc980802 Activation of  1 -Adrenergic Receptor during Ca 2+ Pre-conditioning Elicits Strong Protection against Ca 2+ Overload Injury via Protein Kinase C Signaling Pathway Yigang Wang and Muhammad Ashraf Department of Pathology and Laboratory Medicine, University of Cincinnati Medical Center, Cincinnati, Ohio 45267-0529 USA (Received 13 February 1998, accepted in revised form 17 August 1998) Y. W  M. A. Activation of  1 -Adrenergic Receptor during Ca 2+ Pre-conditioning Elicits Strong Protection Against Ca 2+ Overload Injury via Protein Kinase C Signaling Pathway (1998) 30, 2423–2435. The objective was to test the hypothesis that transient activation of the  1 -adrenergic receptor mimics the beneficial effects of Ca 2+ preconditioning on the Ca 2+ paradox (Ca 2+ PD) injury in rat hearts, and that the protection is mediated by protein kinase C (PKC) signaling pathway. Langendorff-perfused rat hearts were subjected to the Ca 2+ PD (10 min of Ca 2+ depletion followed by 10 min of Ca 2+ repletion). The effects of  1 -adrenergic receptor activation and other interventions on functional, biochemical and pathological changes were assessed. In hearts pretreated with 50 mol/l phenylephrine, left ventricular end-diastolic pressure and coronary flow were significantly preserved after Ca 2+ PD; furthermore, peak loss of lactate dehydrogenase was significantly decreased while ATP was significantly preserved. A remarkable preservation of cell structure was observed in phenylephrine- treated hearts in contrast to non-treated Ca 2+ PD hearts. However, pre-conditioning elicited by phenylephrine caused only a mild improvement in left ventricular developed pressure (LVDP) as opposed to its impressive recovery of left ventricular end-diastolic pressure (LVEDP), heart rate (HR), or coronary flow (CF). The salutary effects of phenylephrine on the Ca 2+ PD injury were almost similar to those observed in hearts which underwent Ca 2+ pre-conditioning (CPC) or were pretreated with 1-stearoyl-2-arachidonoyl-glycerol (SAG), a potent PKC activator. In phenylephrine pretreated hearts, PKC isoform- was localized in the sarcolemma and nucleus, while PKC- and PKC- were localized in the cell membrane, and intercalated disk respectively. Prazosin, a specific  1 - adrenergic receptor antagonist completely abolished the beneficial effects of phenylephrine on the Ca 2+ PD and blocked translocation of PKC isoforms. In addition, prazosin (1 mol/l) also reversed salutary effects of CPC. Moreover, the -adrenergic antagonist, propranolol, had no effect on the protection provided by phenylephrine against the Ca 2+ PD injury. This study suggests that the activation of the  1 -adrenergic receptor confers protection against the lethal injury of the Ca 2+ PD via PKC-mediated signaling pathways. The protection is shared by stimuli common with calcium pre-conditioning.  1998 Academic Press K W:  1 -adrenergic receptor; Ca 2+ paradox; Ca 2+ pre-conditioning; Phenylephrine; Protein kinase C. Ca 2+ , so called Ca 2+ PD (Zimmerman and Introduction Hulsmann, 1996). Ca 2+ is a far more lethal ex- perimental model to study Ca 2+ overload injury Massive cell damage in the heart is observed within seconds when it is initially perfused with a solution than the sustained ischemia/reperfusion. Ca 2+ PD results in the disruption of the electrical and devoid of Ca 2+ followed by perfusate containing Please address all correspondence to: Muhammad Ashraf, Ph.D., Department of Pathology and Laboratory Medicine, University of Cincinnati Medical Center, 231 Bethesda Avenue, Cincinnati, OH 45267-0529, USA. 0022–2828/98/112423+13 $30.00/0  1998 Academic Press