β2-Adrenergic Receptor Agonists Increase Intracellular Free Ca2+ Concentration Cycling in Ventricular Cardiomyocytes through p38 and p42/44 MAPK-mediated Cytosolic Phospholipase A2 Activation

Abstract

We have recently reported that arachidonic acid mediates β 2-adrenergic receptor (AR) stimulation of [Ca2+] i cycling and cell contraction in embryonic chick ventricular cardiomyocytes (Pavoine, C., Magne, S., Sauvadet, A., and Pecker, F. (1999) J. Biol. Chem. 274, 628-637). In the present work, we demonstrate that β 2-AR agonists trigger arachidonic acid release via translocation and activation of cytosolic phospholipase A2 (cPLA2) and increase caffeine-releasable Ca2+ pools from Fura-2-loaded cells. We also show that β2-AR agonists trigger a rapid and dose-dependent phosphorylation of both p38 and p42/44 MAPKs. Translocation and activation of cPLA2, as well as Ca2+ accumulation in sarcoplasmic reticulum stores sensitive to caffeine and amplification of [Ca2+]i cycling in response to β2-AR agonists, were blocked by inhibitors of the p38 or p42/44 MAPK pathway (SB203580 and PD98059, respectively), suggesting a role of both MAPK subtypes in β2-AR stimulation. In contrast, β1-AR stimulation of [Ca2+]i cycling was rather limited by the MAPKs, clearly proving the divergence between β2-AR and β1-AR signaling systems. This study presents the first evidence for the coupling of β2-AR to cardiac cPLA2 and points out the key role of the MAPK pathway in the intracellular signaling elicited by positive inotropic β2-AR agonists in heart.