ATRIAL-NATRIURETIC-PEPTIDE INITIATES CA2+ TRANSIENTS IN ISOLATED RENAL CORTICAL THICK ASCENDING LIMB CELLS

The following studies identified and characterized atrial natriuretic peptide (ANP) receptor-mediated Ca2+ transients in cortical thick ascending limb (CTAL) cells. Primary cell cultures were prepared from porcine kidneys by immunodissection, and intracellular Ca2+ concentration ([Ca2+]i) was determined in single cells with microfluorometry. ANP (10(-7) M) and its analogue, C-type natriuretic peptide (CNP, 10(-7) M), elicited Ca2+ transients [104 +/- 6 (basal levels) to 653 +/- 112 nM (stimulated) and from 84 +/- 4 to 209 +/- 18 nM, respectively]. Receptor-mediated [Ca2+]i increase was dose-dependent with a 50% effective concentration (EC50)) of approximately 10(-10) M. The increment in [Ca2+]i was due to internal release and influx across the plasma membrane. Prior treatment of ANP or CNP (10(-7) M) did not markedly affect a post application of either ANP or CNP. The truncated analogue of ANP, C-ANP-(4-23), which preferentially binds to clearance receptors, elicited an increase in [Ca2+]i (82 +/- 1 to 427 +/- 41 nM). 8-Bromoguanosine 3',5'-cyclic monophosphate (8-BrcGMP) did not alter [Ca2+]i, but pretreatment of CTAL cells with 8-BrcGMP for 30 min before agonist treatment prevented ANP-induced Ca2+ signals [83 +/- 5 (basal) to 88 +/- 5 nM (stimulated)]. These results are evidence for the existence of clearance ANP receptors in CTAL cells that may have biological functions and clearance. The functional responses of these signal interactions may have important consequences on hormone actions with the CTAL.