Type 1 inositol 1,4,5-trisphosphate receptors mediate UTP-induced cation currents, Ca2+signals, and vasoconstriction in cerebral arteries

Abstract

Inositol 1,4,5-trisphosphate receptors (IP3Rs) regulate diverse physiological functions, including contraction and proliferation. There are three IP3R isoforms, but their functional significance in arterial smooth muscle cells is unclear. Here, we investigated relative expression and physiological functions of IP3R isoforms in cerebral artery smooth muscle cells. We show that 2-aminoethoxydiphenyl borate and xestospongin C, membrane-permeant IP3R blockers, reduced Ca2+wave activation and global intracellular Ca2+([Ca2+]i) elevation stimulated by UTP, a phospholipase C-coupled purinergic receptor agonist. Quantitative PCR, Western blotting, and immunofluorescence indicated that all three IP3R isoforms were expressed in acutely isolated cerebral artery smooth muscle cells, with IP3R1 being the most abundant isoform at 82% of total IP3R message. IP3R1 knockdown with short hairpin RNA (shRNA) did not alter baseline Ca2+wave frequency and global [Ca2+]ibut abolished UTP-induced Ca2+wave activation and reduced the UTP-induced global [Ca2+]ielevation by ∼61%. Antibodies targeting IP3R1 and IP3R1 knockdown reduced UTP-induced nonselective cation current ( Icat) activation. IP3R1 knockdown also reduced UTP-induced vasoconstriction in pressurized arteries with both intact and depleted sarcoplasmic reticulum (SR) Ca2+by ∼45%. These data indicate that IP3R1 is the predominant IP3R isoform expressed in rat cerebral artery smooth muscle cells. IP3R1 stimulation contributes to UTP-induced Icatactivation, Ca2+wave generation, global [Ca2+]ielevation, and vasoconstriction. In addition, IP3R1 activation constricts cerebral arteries in the absence of SR Ca2+release by stimulating plasma membrane Icat.