β2-Adrenergic Receptor (β2-AR) Stimulation of Cytosolic Phospholipase A2 (cPLA2) Is Dependent on PKC and IP3-Mediated Ca2+ Signaling in Atrial Myocytes

We reported that inhibition of adenylate cyclase (AC)/cAMP by cell attachment to laminin (+LMN) or pharmacological (KT5720) inhibition of cAMP-dependent protein kinase (PKA) in cells not attached to LMN (-LMN-PKA), activates β2-AR stimulation of ICa,L via cPLA2 signaling. The present study determined the role of PKC and IP3-mediated Ca2+ release in β2-AR/cPLA2 signaling. As previously reported, 0.1 μM zinterol (β2-AR agonist) stimulation of L-type Ca2+ current (ICa,L) was unaffected by 10 μM AACOCF3 (cPLA2 inhibitor) in cells not attached to LMN (-LMN) but was significantly inhibited in +LMN and -LMN-PKA myocytes. Zinterol stimulation of ICa,L in -LMN-PKA myocytes was blocked by 5 μM U73122 (PLC inhibitor) and significantly inhibited by 4 μM chelerythrine (PKC inhibitor). Zinterol stimulation of ICa,L in -LMN myocytes was unaffected by inhibition of IP3-receptors (IP3Rs) by 2 μM 2-APB, but was significantly inhibited in +LMN and -LMN-PKA myocytes. Cells were cultured on LMN (24 hrs) with an adenovirus IP3 affinity trap to inhibit IP3-dependent Ca2+ signaling. Compared to control cells (β-gal), zinterol stimulation of ICa,L was significantly inhibited in cells infected with IP3 trap. Laser scanning confocal microscopy (fluo-4) revealed that zinterol stimulation of +LMN myocytes elicited local intracellular Ca2+ release events in 1 mM tetracaine (blocks RyR Ca2+ release), that were blocked by 2-APB. We conclude that inhibition of cAMP/PKA activates β2-AR stimulation of ICa,L via cPLA2 which is dependent on PKC and IP3-mediated Ca2+ signaling. These findings may be relevant to the remodeling of β-AR signaling in diseased (fibrotic) and/or aging atria, both of which exhibit decreases in AC activity.