Subcellular localization of phospholipase C isoforms in vascular smooth muscle

Abstract

The phospholipase C (PLC) isoform most important during agonist-activated IP 3 production in vascular smooth muscle is still unknown. When PLC activity in rat tail artery homogenate was determined, this activity was shown to be inhibited by an antibody directed against PLCβ2. Antibodies directed against the γ1, β1, β3 and δ1 isoforms of PLC failed to inhibit PLC activity in this tissue. Both PLCβ2 and PLCγ1 were isolated from rat tail artery by DEAE column chromatography and PLCβ2 activity was shown to be 3-fold greater than PLCγ1 activity. When rat tail artery was treated with norepinephrine (10 mM), PLCβ2 was shown to translocate from cytosol to membranes. When subcellular fractions of rat tail artery were isolated by sucrose density gradient centrifugation, including nuclei, plasma membrane, and cytosol, PLCβ2 was detected in the plasma membrane and the cytosol but not in the nuclei. PLCδ1 and PLCγ1 were found only in cytosol. This evidence is consistent with the model wherein an agonist such as norepinephrine can activate smooth muscle contraction via interaction with a plasma membrane receptor which can easily interact with a plasma membrane-associated isoform of PLC, such as PLCβ2.