Different phospholipase-C-coupled receptors differentially regulate capacitative and non-capacitative Ca²⁺ entry in A7r5 cells

Several receptors, including those for AVP (Arg⁸-vasopressin) and 5-HT (5-hydroxytryptamine), share an ability to stimulate PLC (phospholipase C) and so production of IP₃ (inositol 1,4,5-trisphosphate) and DAG (diacylglycerol) in A7r5 vascular smooth muscle cells. Our previous analysis of the effects of AVP on Ca²⁺ entry [Moneer, Dyer and Taylor (2003) Biochem. J. 370, 439–448] showed that arachidonic acid released from DAG stimulated NO synthase. NO then stimulated an NCCE (non-capacitative Ca²⁺ entry) pathway, and, via cGMP and protein kinase G, it inhibited CCE (capacitative Ca²⁺ entry). This reciprocal regulation ensured that, in the presence of AVP, all Ca²⁺ entry occurred via NCCE to be followed by a transient activation of CCE only when AVP was removed [Moneer and Taylor (2002) Biochem. J. 362, 13–21]. We confirm that, in the presence of AVP, all Ca²⁺ entry occurs via NCCE, but 5-HT, despite activating PLC and evoking release of Ca²⁺ from intracellular stores, stimulates Ca²⁺ entry only via CCE. We conclude that two PLC-coupled receptors differentially regulate CCE and NCCE. We also address evidence that, in some A7r5 cells lines, AVP fails either to stimulate NCCE or inhibit CCE [Brueggemann, Markun, Barakat, Chen and Byron (2005) Biochem. J. 388, 237–244]. Quantitative PCR analysis suggests that these cells predominantly express TRPC1 (transient receptor potential canonical 1), whereas cells in which AVP reciprocally regulates CCE and NCCE express a greater variety of TRPC subtypes (TRPC1=6>2>3).