AJP - Renal Physiology, Vol 265, Issue 2 272-F277, Copyright © 1993 by American Physiological Society

ARTICLES

Osmolarity-stimulated urea transport in rat terminal IMCD: role of intracellular calcium

A. G. Gillin, R. A. Star and J. M. Sands
Department of Medicine, Emory University School of Medicine, Atlanta, Georgia 30322.

We showed previously that both increasing osmolality by adding NaCl or manitol (hyperosmolarity) or adding vasopressin can stimulate urea permeability in rat terminal inner medullary collecting ducts (IMCD). Vasopressin acts via adenosine 3',5'-cyclic monophosphate (cAMP), but the mechanism by which hyperosmolarity acts is unknown. To study the mechanism, we determined the effect of varying osmolality (with NaCl) on two potential second messenger systems, i.e., cAMP and intracellular calcium. There was no significant difference in cAMP production among tubules incubated at 290, 490, 690, or 890 mosmol/kg. In contrast, cAMP did increase significantly after vasopressin (10(-8) M) addition. Intracellular calcium increased significantly when osmolality was increased from 290 to 490 mosmol/kg in the absence of vasopressin. To examine whether changes in intracellular calcium affect urea permeability, we added thapsigargin (and removed bath calcium) while maintaining osmolality at 290 mosmol/kg. Both intracellular calcium and urea permeability increased significantly. Next, we buffered intracellular calcium by pretreatment with the acetoxymethyl ester of 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA, 50 microM). BAPTA completely blocked the increase in urea permeability occurring when osmolality was increased from 290 to 490 mosmol/kg, but did not block the increase in urea permeability occurring when vasopressin (10(-8) M) was added. In summary, 1) hyperosmolarity increases intracellular calcium, but has no effect on cAMP accumulation; 2) thapsigargin increases intracellular calcium and urea permeability; and 3) BAPTA blocks the hyperosmolarity-stimulated increase in urea permeability, but not vasopressin-stimulated urea permeability.(ABSTRACT TRUNCATED AT 250 WORDS)

This article has been cited by other articles:

				N. W. Blessing, M. A. Blount, J. M. Sands, C. F. Martin, and J. D. Klein Urea transporters UT-A1 and UT-A3 accumulate in the plasma membrane in response to increased hypertonicity Am J Physiol Renal Physiol, November 1, 2008; 295(5): F1336 - F1341. [Abstract] [Full Text] [PDF]

				M. B. Burg, J. D. Ferraris, and N. I. Dmitrieva Cellular Response to Hyperosmotic Stresses Physiol Rev, October 1, 2007; 87(4): 1441 - 1474. [Abstract] [Full Text] [PDF]

				G. S. Stewart, S. L. King, E. A. Potter, and C. P. Smith Acute regulation of mUT-A3 urea transporter expressed in a MDCK cell line Am J Physiol Renal Physiol, April 1, 2007; 292(4): F1157 - F1163. [Abstract] [Full Text] [PDF]

				V. Pech, J. D. Klein, S. D. Kozlowski, S. M. Wall, and J. M. Sands Vasopressin increases urea permeability in the initial IMCD from diabetic rats Am J Physiol Renal Physiol, September 1, 2005; 289(3): F531 - F535. [Abstract] [Full Text] [PDF]

				A. Kato, J. D. Klein, C. Zhang, and J. M. Sands Angiotensin II increases vasopressin-stimulated facilitated urea permeability in rat terminal IMCDs Am J Physiol Renal Physiol, November 1, 2000; 279(5): F835 - F840. [Abstract] [Full Text] [PDF]

				T. Inoue, J. Terris, C. A. Ecelbarger, C.-L. Chou, S. Nielsen, and M. A. Knepper Vasopressin regulates apical targeting of aquaporin-2 but not of UT1 urea transporter in renal collecting duct Am J Physiol Renal Physiol, April 1, 1999; 276(4): F559 - F566. [Abstract] [Full Text] [PDF]

				J. M. SANDS Regulation of Renal Urea Transporters J. Am. Soc. Nephrol., March 1, 1999; 10(3): 635 - 646. [Abstract] [Full Text]

				F. LANG, G. L. BUSCH, M. RITTER, H. VOLKL, S. WALDEGGER, E. GULBINS, and D. HAUSSINGER Functional Significance of Cell Volume Regulatory Mechanisms Physiol Rev, January 1, 1998; 78(1): 247 - 306. [Abstract] [Full Text] [PDF]