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

Zhao G, Adebiyi A, Blaskova E, Xi Q, Jaggar JH. Type 1 inositol 1,4,5-trisphosphate receptors mediate UTP-induced cation currents, Ca2+ signals, and vasoconstriction in cerebral arteries. Am J Physiol Cell Physiol 295: C1376-C1384, 2008. First published September 17, 2008; doi: 10.1152/ajpcell.00362.2008.-Inositol 1,4,5-trisphosphate receptors (IP(3)Rs) 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 IP(3)R1 being the most abundant isoform at 82% of total IP3R message. IP(3)R1 knockdown with short hairpin RNA (shRNA) did not alter baseline Ca2+ wave frequency and global [Ca2+](i) but abolished UTP-induced Ca2+ wave activation and reduced the UTP-induced global [Ca2+](i) elevation by similar to 61%. Antibodies targeting IP(3)R1 and IP(3)R1 knockdown reduced UTP-induced nonselective cation current (I-cat) activation. IP(3)R1 knockdown also reduced UTP-induced vasoconstriction in pressurized arteries with both intact and depleted sarcoplasmic reticulum (SR) Ca2+ by similar to 45%. These data indicate that IP(3)R1 is the predominant IP3R isoform expressed in rat cerebral artery smooth muscle cells. IP(3)R1 stimulation contributes to UTP-induced I-cat activation, Ca2+ wave generation, global [Ca2+](i) elevation, and vasoconstriction. In addition, IP(3)R1 activation constricts cerebral arteries in the absence of SR Ca2+ release by stimulating plasma membrane I-cat.