AJP - Cell Physiology, Vol 257, Issue 6 C1093-C1100, Copyright © 1989 by American Physiological Society
Proximal tubule volume regulation in hyperosmotic media: intracellular K+, Na+, and Cl-
L. Rome, J. Grantham, V. Savin, J. Lohr and C. Lechene
Department of Medicine, University of Kansas Medical Center, Kansas City 66103.
Nonperfused proximal S2 segments from rabbit kidney cortex have been shown
to keep cell volume constant as medium osmolality is slowly raised but to
shrink and not exhibit regulatory volume increase (RVI) if medium
osmolality is abruptly elevated (J. Lohr and J. Grantham. J. Clin. Invest.
78: 1165-1172, 1986). In the current study, 0.5 mM butyrate in the medium
1) extended the range from 361 to 450 mosmol/kgH2O over which cells
maintained volume constant as osmolality was gradually raised and 2)
restored RVI after cell shrinkage when osmolality was rapidly raised from
295 to 400 mosmol/kgH2O. Volume regulation was associated with net
increases in intracellular Na+ and Cl- but no change in K+ (measured by
electron probe). The increments in Na+ and Cl- were insufficient to account
for the total addition of osmolytes required for volume maintenance or
restoration. The fraction of the expected increase in intracellular osmoles
accounted for by the increase in [(K+)i + (Na+)i + (Cl-)i] was 52 and 21%
for gradual and rapid osmotic changes, respectively. We conclude that
butyrate enhances the capacity of S2 segments to regulate volume in
hyperosmotic medium by promoting addition of Na+ and Cl- and by other
undermined factors.
