Evidence for dual signalling pathways for v2 vasopressin receptor
in rat inner medullary collecting duct.
Ecelbarger, Carolyn A., Chung-Lin Chou, Stephen J. Lolait, Mark A.
Knepper, and Susan R. Digiovanni.
Laboratory of Kidney and Electrolyte Metabolism, National Heart,
Lung and Blood Institute, National Institutes of Health, Bethesda, MD
20892 and Laboratory of Cell Biology, National Institute of Mental
Health, National Institutes of Health, Bethesda, MD 20892
APStracts 2:0195F, 1995.
Previous studies have demonstrated that both the V2 receptor agonist,
dDAVP and the V1a receptor agonist, [Phe2,Orn8]-vasotocin, (PO-VT)
increase intracellular calcium [Ca2+]i in the rat inner medullary
collecting duct (IMCD). The present studies were done to clarify the
receptor subtype(s) responsible for calcium mobilization.
Measurements of [Ca2+]i using fura-2 in microdissected IMCD segments,
confirmed that AVP, dDAVP, and PO-VT stimulate an increase in [Ca2+]i
and that the response to all three agents could be blocked by the
specific V2-receptor antagonist, d(CH2)5[D-Ile2,Ile4,Arg8]
-vasopressin, (II-VP). These results would suggest that all three
agents acted through the V2 receptor. Furthermore, we showed that PO
-VT increased cyclic AMP production in IMCD suspensions and water
permeability in isolated perfused tubules. These responses were also
blocked by II-VP indicating that PO-VT is also a V2 agonist in the
IMCD. Finally, we utilized the quantitative RT-PCR technique of
Wiesner [39] to evaluate V1a and V2 mRNA levels in rat collecting
duct. In terminal IMCD, we estimated > 30 copies/cell for V2
receptor mRNA, but less than 1 copy/cell of V1a receptor mRNA, thus
there is little or no V1a mRNA expression in the terminal IMCD. These
results suggest that calcium mobilization in response to vasopressin
analogues is associated with the V2 receptor, and that the V2
receptor is linked to both adenylyl cyclase and calcium mobilization
in the rat IMCD.
Received 25 May 1995; accepted in final form 18 October 1995.
APS Manuscript Number F165-5.
Article publication pending Am. J. Physiol. (Renal Fluid Electrolyte
Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 6 November 95