Juxtaglomerular cell CaSR stimulation decreases renin release via activation of the PLC/IP₃pathway and the ryanodine receptor

Abstract

The calcium-sensing receptor (CaSR) is a G-coupled protein expressed in renal juxtaglomerular (JG) cells. Its activation stimulates calcium-mediated decreases in cAMP content and inhibits renin release. The postreceptor pathway for the CaSR in JG cells is unknown. In parathyroids, CaSR acts through Gq and/or Gi. Activation of Gq stimulates phospholipase C (PLC), and inositol 1,4,5-trisphosphate (IP3), releasing calcium from intracellular stores. Gi stimulation inhibits cAMP formation. In afferent arterioles, the ryanodine receptor (RyR) enhances release of stored calcium. We hypothesized JG cell CaSR activation inhibits renin via the PLC/IP3 and also RyR activation, increasing intracellular calcium, suppressing cAMP formation, and inhibiting renin release. Renin release from primary cultures of isolated mouse JG cells (n ϭ 10) was measured. The CaSR agonist cinacalcet decreased renin release 56 Ϯ 7% of control (P Ͻ 0.001), while the PLC inhibitor U73122 reversed cinacalcet inhibition of renin (104 Ϯ 11% of control). The IP3 inhibitor 2-APB also reversed inhibition of renin from 56 Ϯ 6 to 104 Ϯ 11% of control (P Ͻ 0.001). JG cells were positively labeled for RyR, and blocking RyR reversed CaSR-mediated inhibition of renin from 61 Ϯ 8 to 118 Ϯ 22% of control (P Ͻ 0.01). Combining inhibition of IP3 and RyR was not additive. Gi inhibition with pertussis toxin plus cinacalcet did not reverse renin inhibition (65 Ϯ 12 to 41 Ϯ 8% of control, P Ͻ 0.001). We conclude stimulating JG cell CaSR activates G q, initiating the PLC/IP3 pathway, activating RyR, increasing intracellular calcium, and resulting in calcium-mediated renin inhibition. calcium; renin; calcium-sensing receptor; inositol-3 phosphate; phospholipase C; protein kinase A; ryanodine receptor THE CALCIUM-SENSING RECEPTOR (CaSR) is a G protein-coupled 7-transmembrane receptor (33) found in the parathyroid gland, blood vessels, and kidney (18). In the parathyroid gland where CaSR was first described, high extracellular calcium results in decreased parathyroid hormone secretion (21). This is mediated by calcium activation of the CaSR, stimulating the G proteins G q and/or G i . In the parathyroid, activation of G q stimulates phospholipase C (PLC), producing diacylglycerol and inositol 1,4,5-trisphosphate (IP 3 ), the latter of which releases calcium from intracellular stores bound in the endoplasmic reticulum (ER) (48). G i stimulation leads to the inhibition of cAMP formation (16,48). Either pathway results in suppressing parathyroid hormone release.In the secretory juxtaglomerular (JG) cells, like the parathyroids, increased calcium results in the suppression of renin secretion (21,43,44). We have previously reported, both in vitro (44) and in vivo (6), that the JG cells contain CaSR, and that increased media calcium or activation of the CaSR with a calcimimetic (6, 43, 44) leads to suppression of renin secretion. JG cells synthesize, store, and release renin, the rate-limiting enzyme involved in the formation of angiotensin II (9). The cyclic nucleotide cAMP ...

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Adenosine inhibits renin release from juxtaglomerular cells via an A1 receptor-TRPC-mediated pathway

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