Molecular Mechanisms for Activation of Voltage-independent Ca2+ Channels by Endothelin-1/Endothelin-A Receptors

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Endothelin-1 (ET-1) activates two types of Ca2+- permeable non-selective cation channels (designated NSCC-1 and NSCC-2) and a store-operated Ca2+ channel (SOCC) in Chinese hamster ovary cells expressing endothelin-A receptors (CHOETAR), which couple with Gq, Gs and G12. The purpose of this study was to identify the G proteins involved in the activation of these Ca2+ channels, using mutated ETARs with coupling to either Gq or Gs/G12 (designated ETARδ385 and SerETAR, respectively) and a dominant negative mutant of G12 (G12G228A). ETARδ385 is truncated downstream of Cys385 in the C-terminal as palmitoylation sites, whereas SerETAR is unpalmitoylated because of substitution of all the cysteine residues to serine (Cys383Cys385-388 → Ser383Ser385-388). ET-1 activated SOCC in CHO-ETARδ385. In CHO-SerETAR or CHO-ETAR pretreated with U73122, an inhibitor of phospholipase C, ET-1 activated NSCC-1. ET-1 activated SOCC in CHO-ETAR microinjected with G12G228A. Moreover, ET-1 activated NSCC-1 in CHO-ETAR treated with LY 294002, the phosphoinositide 3-kinase inhibitor. These results indicate that NSCC-1 is activated via a G12-dependent pathway, NSCC-2 via Gq/phospholipase C-dependent and G12-dependent pathways, and SOCC via a Gq-phospholipase C-dependent pathway. In addition, NSCC-2 and SOCC are stimulated by ET-1 via a phosphoinositide 3-kinase-dependent cascade, whereas NSCC-1 is stimulated via a phosphoinositide 3-kinase-independent cascade.

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