Activation of h+-atpase by hypotonicity: a novel regulatory
mechanism for h+ secretion in inner medullary collecting duct.
Amlal, Hassane, Akhil Goel, and Manoocher Soleimani.
Department of Medicine, University of Cincinnati School of
Medicine, and Veterans Affairs Medical Center, Cincinnati, Ohio
45267-585
APStracts 5:0116F, 1998.
The effect of hypotonicity on H+-ATPase activity was examined in
cultured inner medullary collecting duct (mIMCD-3) cells. mIMCD-3
cells were grown to confluence, loaded with BCECF, and assayed for
H+-ATPase activity as the Na+ and K+-independent pHi recovery
following an acid load. Exposure of mIMCD-3 cells to a hypotonic
solution (150 mosmol/kg H2O) increased pHi recovery by 350%
(p<0.0001). This effect was inhibited by DES (an inhibitor of H+
-ATPase) and was not dependent on external K+, indicating lack of
involvement of H+-K+-ATPase. H+-ATPase activation was acute,
independent of cell calcium, and was not secondary to Cl- channel
activation. The magnitude of H+-ATPase up-regulation was dependent on
the osmolarity of the media, with maximum stimulation at 150 mOsm/kg
H2O. H+-ATPase up-regulation in hypotonicity was significantly
blocked in the presence of staurosporine or calphostin C, or in cells
pretreated with PMA, indicating involvement of protein kinase C.
Hypotonicity inhibited the Na+/H+ exchanger activity in mIMCD-3
cells, indicating that its stimulatory effect is specific to H+
-ATPase. In conclusion, a novel regulatory mechanism of H+-ATPase by
hypotonicity is described. The increased H+-ATPase activity in
hypotonicity may be responsible for increased HCO3- reabsorption and
maintained acid-base homeostasis in hypo-osmolar states.
Received 3 March 1998; accepted in final form 26 June 1998.
APS Manuscript Number F48-8.
Article publication pending Am. J. Physiol. (Renal Physiology).
ISSN 1080-4757 Copyright 1998 The American Physiological Society.
Published in APStracts on 30 July 1998