cAMP-dependent effects of vasopressin and calcitonin on cytosolic calcium in rat CCD.
Fura 2 fluorescence measurements were carried out on microperfused rat cortical collecting ducts (CCD) to investigate the effect of adenosine 3',5'-cyclic monophosphate (cAMP) and adenylate cyclase-stimulating hormones on free cytosolic calcium ([Ca2+]i). Forskolin, 3-isobutyl-1-methylxanthine, and 8-(4-chlorophenylthio)-cAMP (CPT-cAMP) all triggered marked and sustained [Ca2+]i variations. Maximal increases elicited by 100 microM CPT-cAMP amounted to 101 +/- 11 nM (mean +/- SE, n = 18). This effect was mostly dependent on the presence of basolateral calcium and totally independent of luminal calcium. It remained unchanged in CCD perfused with sodium-free luminal fluid (82 +/- 10 nM, n = 5), pretreated with 1 mM bath ouabain (113 +/- 20, n = 4), or superfused with sodium-free bath in the presence of ouabain (82 +/- 22, n = 5). The V2 agonist 1-desamino-8-D-arginine vasopressin (DDAVP, 10 nM) increased [Ca2+]i by 57 +/- 5 nM (n = 27), a value 40% lower than that achieved with 10 nM AVP (141 +/- 7, n = 34) but similar to that observed with AVP + a V1a antagonist (57 +/- 6, n = 6). Significant effects could also be obtained with 200 pM DDAVP (31 +/- 6, n = 8) and arginine vasopressin (AVP) (72 +/- 6, n = 16). Rat calcitonin also raised [Ca2+]i by 43 +/- 10 (n = 8) and 66 +/- 8 nM (n = 17) at 1 and 10 nM, respectively, and its effect was not additive to that of CPT-cAMP. Calcitonin and DDAVP effects, like those of CPT-cAMP and forskolin, were nearly abolished in Ca(2+)-free bath, but AVP action on intracellular release persisted. These results show that, in rat CCD, cAMP effects on [Ca2+]i mainly result from basolateral calcium entry. In contrast to rabbit CCD the mechanism is independent on Na reabsorption and basolateral Na+/Ca2+ exchange. Calcitonin and DDAVP effects on [Ca2+]i are probably secondary to increased cAMP production.
Siga
E
E
Laboratoire de Physiologie Cellulaire, Collège de France, Paris.
Champigneulle
A
A
Imbert-Teboul
M
M
D000262:Adenylyl Cyclases / Q000378:metabolism; D000818:Animals; D001127:Arginine Vasopressin / Q000494:pharmacology*; D002116:Calcitonin / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism; D000242:Cyclic AMP / Q000378:metabolism / Q000502:physiology*; D003600:Cytosol / Q000378:metabolism*; D007685:Kidney Tubules, Collecting / Q000166:cytology / Q000378:metabolism*; D008297:Male; D009994:Osmolar Concentration; D051381:Rats; D017207:Rats, Sprague-Dawley; D019831:Sodium-Calcium Exchanger
D002352:Carrier Proteins; D019831:Sodium-Calcium Exchanger; D001127:Arginine Vasopressin; D002116:Calcitonin; D000242:Cyclic AMP; D000262:Adenylyl Cyclases; D002118:Calcium