Vasopressin and oxytocin receptors coupled to Ca2+ mobilization in rat inner medullary collecting duct.
In renal collecting duct epithelial cells, arginine vasopressin (AVP) at greater than nanomolar concentrations has been reported to transiently increase intracellular free calcium ([Ca2+]i) in a manner consistent with activation of the phosphoinositide pathway. To investigate whether any of the known neurohypophysial hormone subtypes are involved, we measured [Ca2+]i in microdissected rat terminal inner medullary collecting duct (IMCD) using fura-2. To allow quantitative comparisons of the response under different conditions, we determined the areas under the response curves (in nM.min) over 1.5 min using numerical integration. AVP, the V1b-receptor agonist [deamino1,D-3-(pyridyl)Ala2,Arg8]vasopressin, the V2-receptor agonist 1-desamino-8-D-arginine vasopressin, oxytocin, and the selective oxytocin-receptor agonist [Thr4,Gly7]oxytocin (TG-OXT), each at 10 nM, significantly increased [Ca2+]i (69.52 +/- 10.25, 27.0 +/- 11.7, 24.33 +/- 5.83, 14.75 +/- 2.81, and 14.57 +/- 3.50 nM.min, respectively). In contrast, a V1a-selective agonist ([Phe2,Ile3,Orn8]vasopressin) did not increase [Ca2+]i (0.43 +/- 2.36 nM.min). In desensitization studies, challenge with 10 nM AVP or TG-OXT completely prevented a rise in [Ca2+]i in response to immediate rechallenge with the same agent, but not the other, demonstrating homologous desensitization. The lack of cross-desensitization implies that at least two receptors are present that can trigger a rise in [Ca2+]i in response to neurohypophysial hormones. Antagonists for oxytocin ([des-glycinamide9,d(CH2)5(1),O-Me-Tyr2,Thr4,Orn8]vaso tocin), V2 ([d(CH2)5(1),D-Ile2,Ile4,Arg8]vasopressin), and V1a ([d(CH2)5(1),O-Me-Tyr2,Arg8]vasopressin) receptors partially inhibited the [Ca2+]i response induced by 10 nM AVP (89.5, 81.6, and 51.4% inhibition, respectively). These data are consistent with the view that both an oxytocin receptor and a vasopressin receptor are coupled to a [Ca2+]i mobilization response in rat terminal IMCD. This vasopressin receptor is distinct from both the V1a receptor and the V2 receptor and may be either the V1b receptor or a novel vasopressin receptor subtype.
Maeda
Y
Y
Laboratory of Kidney and Electrolyte Metabolism, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland 20892.
Han
J S
JS
Gibson
C C
CC
Knepper
M A
MA
D000818:Animals; D065092:Antidiuretic Hormone Receptor Antagonists; D001127:Arginine Vasopressin / Q000494:pharmacology; D001692:Biological Transport; D002118:Calcium / Q000378:metabolism*; D007425:Intracellular Membranes / Q000378:metabolism; D007679:Kidney Medulla; D007685:Kidney Tubules, Collecting / Q000378:metabolism*; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D018045:Receptors, Oxytocin; D017483:Receptors, Vasopressin / Q000378:metabolism*
D065092:Antidiuretic Hormone Receptor Antagonists; D018045:Receptors, Oxytocin; D017483:Receptors, Vasopressin; D001127:Arginine Vasopressin; D002118:Calcium