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Potential Role of PP2A in Regulating Ca2+‐Activated Cl− Channels in Pulmonary Artery Smooth Muscle Cells

Ca2+‐activated Cl− currents (IClCa) represent a major excitatory mechanism in vascular smooth muscle cells (SMCs). Our group previously showed that CaMKII and Calcineurin (CaN) exert opposed regulatory effects on IClCa in arterial SMCs. In this study, we determined whether other phosphatases also modulate IClCa in rabbit pulmonary artery (PA) myocytes. In a previous study, our group (Ayon et al., Faseb J. 22: 937.16, 2008) detected significant mRNA and protein expression of multiple isoforms for PP1, PP2A and PP2B in rabbit PA tissue homogenates. Recently, we have extended our studies to show significant cytoplasmic immunolabeling of PP1α, PP1β/d, PP1γ, and PP2A in isolated PASMCs. Results from previous patch clamp experiments on freshly isolated PA myocytes (Ayon et al., Faseb J. 22: 937.16, 2008) showed differential responses when manipulating endogenous PP1 and PP2A as opposed to supplying these phosphatases exogenously. To address this issue we examined the effects of Fostriecin (FOS), a highly specific inhibitor of PP2A, on an exogenous application of PP2A in the presence of ATP. Cells dialyzed with 150 nM FOS produced a delayed but pronounced block of exogenous PP2A‐induced recovery of IClCa which contrasted with the inability of FOS to alter the recovery of IClCa evoked by endogenous phosphatase(s). These results suggest that endogenous PP1 and CaN, not PP2A, are involved in IClCa regulation in PASMCs.