Some effects of monovalent anion replacement on the volume and composition of cells in incubated slices of rat renal cortex

Anion-induced dynamic behavior of apical water channels in vasopressin-sensitive epithelia exposed to mercury

We showed recently that, in toad skins preexposed to Hg, water permeability is high in SO4-Ringer and low in Cl-Ringer. This anion effect was further investigated in Hg-treated skins and bladders of toads (Bufo marinus) in a variety of experimental conditions, including glutaraldehyde fixation and stimulation by vasopressin (VP) or isoproterenol (IP). In fixed bladders either unstimulated or stimulated with VP, net water flow (Jw) in SO4-Ringer [Jw (SO4)] was always significantly higher than Jw in Cl [Jw (Cl)]; the same applies to fixed toad skins, either unstimulated or stimulated with IP. In unfixed isolated toad epidermis challenged with IP before Hg exposure, Jw(SO4)/Jw(Cl) >> 1 approaching the ratio Jw (maximally stimulated)/Jw (basal). Therefore, anion-induced Jw changes were present whether Hg acted on epithelial water channels exocytosed by Hg itself or by hydrosomotic agents and suggest a switching between open and closed configurations of the channel protein. This anion effect was not abolished by glutaraldehyde and might be correlated with changes in intracellular chloride.

Propionate induces cell swelling and K+ accumulation in shark rectal gland

Small organic anions have been reported to induce cell solute accumulation and swelling. To investigate the mechanism of swelling, we utilized preparations of rectal gland cells from Squalus acanthias incubated in medium containing propionate. Propionate causes cells to swell by diffusing across membranes in its nonionic form, acidifying cell contents, and activating the Na+-H+ antiporter. The Na+-H+ exchange process tends to correct intracellular pH (pHi), and thus it maintains a favorable gradient for propionic acid diffusion and allows propionate to accumulate. Activation of the Na+-H+ antiport also facilitates Na+ entry into the cell and Nai accumulation. At the same time Na+-K+-ATPase activity, unaffected by propionate, replaces Nai with Ki, whereas the K+ leak rate, decreased by propionate, allows Ki to accumulate. As judged by 86Rb+ efflux, the reduction in K+ leak was not due to propionate-induced cell acidification or reduction in Cli concentration. Despite inducing cell swelling, propionate did not disrupt cell structural elements and F actin distribution along cell membranes.

An inwardly-directed sodium-amino acid cotransporter influences steady-state cell volume in slices of rat renal papilla incubated in hyperosmotic media

The effect of a neutral amino acid, 2-aminoisobutyric acid (AIB) on steady state cell volume has been examined in rat renal papillary slices incubated in hyperosmotic media (2,000 mosmol/kg H2O) containing high concentrations of NaCl and urea (thus imitating papillary interstitial fluid in the intact kidney during antidiuresis). Volumes were significantly increased (P less than 0.001) when external AIB was raised from 0.1 to 10 mmol/l. Na+-dependent AIB uptake occurred, and there were net increases in cell contents of Na+ and Cl-. Replacement of Na+ by Li+, but not by other cations, did not influence the effect of AIB concentration on cell volume, but this was abolished when Cl- was replaced by other anions. The effect of AIB was abolished by diphenylamine-2-carboxylate (10(-3) mmol/l), bumetanide (at 1 mmol/l but not 10(-2) mmol/l) and by N,N'-dicyclohexylcarbodiimide (0.5 mmol/l), but not by amiloride (1 mmol/l) or 4-acetamido-4'-iso-thiocyanato-stilbene-2,2'-disulphonic acid (1 mmol/l), and was enhanced by the presence of Ba2+ or quinine (1 mmol/l). The findings are interpreted in terms of an inwardly-directed Na+-amino acid cotransporter, which determines steady-state volume, requires simultaneous entry of Cl- through conductive pathways, and whose effects on cell volume are moderated by K+ efflux through volume-sensitive K+ channels.