Effects of replacing medium sodium by choline, caesium, or rubidium, on water and ion contents of renal cortical slices

Abstract

SUMMARY1. Renal cortical slices from rat, rabbit, and guinea-pig were incubated in media in which choline, caesium or rubidium replaced sodium.2. Slices of rabbit and guinea-pig renal cortex incubated in oxygenated choline Ringer decreased in volume initially and did not swell over 3 hr at 250 C. There was a steady loss of potassium. Inhibition of metabolism (N2 +1 mM iodoacetamide) caused some swelling. Ouabain, 10 mm, in choline Ringer affected neither loss of potassium nor tissue water content.3. Slices of rat renal cortex similarly incubated in choline Ringer swelled over 3 hr at 250 C whether or not metabolism was inhibited; ouabain (15 mM) affected neither tissue potassium loss nor tissue water content.4. Incubation in choline Ringer containing either 0-2 mm p-chloromercuribenzoic acid, or 1 mm ethacrynic acid increased the tissue water content of guinea-pig renal cortical slices.5. Depletion of cellular potassium (by preliminary incubation in oxygenated potassium-free sodium Ringer with 10 mm ouabain at 300 C) resulted in increased tissue water content when rabbit renal cortical slices were subsequently incubated in oxygenated choline Ringer at 250 C for 3 hr.6. There was no evidence of energy-dependent extrusion of water or ions from either equilibrated rat or rabbit renal cortical slices leached at 0.50 C and then reincubated at 250 C in choline Ringer.7. Rat and guinea-pig renal cortical slices leached at 0.50 C and reincubated at 250 C swelled in rubidium Ringer and in caesium Ringer. There was no evidence of energy-dependent water or ion extrusion when metabolism was restored after leaching in either of these media. Metabolizing rat slices but not guinea-pig slices swelled faster than slices whose metabolism was inhibited. P. M. HUGHES AND A. D. C. MACKNIGHT 8. These results lend no support to the mechano-chemical hypothesis which ascribes cellular volume regulation to a contractile mechanism squeezing isotonic extracellular fluid from the cells. Instead it is suggested that cellular water content in these experiments reflects the balance between the rate of loss of potassium (and chloride) from the cells and the rate of uptake of extracellular cation (and chloride) into the cells -these rates reflecting both the electrochemical potential gradients of the ions and membrane permeability to them. The implications in relation to the hypothesis of ouabain-insensitive cellular volume regulation are discussed.

Sodium‐hydrogen ion exchange in rabbit renal cortical slices incubated in acetate media.

“…Thus we cannot attribute the S,ICES IN ACETATE MEDIA relative lack of swelling in choline media to choline transport by the sodium pump. This conclusion is supported by the finding that cell water content in slices incubated in choline chloride medium (Hughes & Macknight, 1977) or in choline acetate medium (Table 2) did not increase in the presence of ouabain. Having established the behaviour of slices in choline acetate medium, we examined the effects on slices of low concentrations of sodium in 132 mM-acetate media maintained isosmotic by choline.…”

“…However, cell potassium content was remarkably well maintained, when compared to the values in sodium chloride medium, though the associated cell swelling lowered the estimated potassium concentration (113 mm compared to 150 mm for cells incubated in sodium chloride medium). The reduced swelling of slices incubated in isosmotic choline acetate medium was similar to the relative lack of swelling of renal cortical slices incubated in isosmotic choline chloride medium (Hughes & Macknight, 1977). In particular, in these earlier studies, metabolizing rabbit kidney slices, after an initial small loss of water, maintained a remarkably constant water content over 180 min of incubation ( Table 2, Hughes & Macknight, 1977).…”

“…The reduced swelling of slices incubated in isosmotic choline acetate medium was similar to the relative lack of swelling of renal cortical slices incubated in isosmotic choline chloride medium (Hughes & Macknight, 1977). In particular, in these earlier studies, metabolizing rabbit kidney slices, after an initial small loss of water, maintained a remarkably constant water content over 180 min of incubation ( Table 2, Hughes & Macknight, 1977). The relative lack of cell swelling in both choline acetate and choline chloride media and the maintenance of a relatively high cell potassium content could be explained if choline were able to substitute for sodium in activating the Na+-K+-ATPase and thus be transported by the sodium pump.…”

Anion exchange and volume regulation during metabolic blockade of renal cortical slices.

“…Data supporting this theory of cell volume regulation include (1) increases in cell volume often but not invariably observed after metabolic inhibition (Leaf, 1956;Heckman & Parsons, 1959;Okamoto & Quastel, 1970;Grochowski, Ganote, Hill & Jennings, 1976;Hughes & Macknight, 1977;Pine, Bing, Weintraub & Abelmann, 1979); (2) increases in cell volume when sodium is replaced by a cation to which the cell membrane is permeable and which cannot be actively extruded (Boyle & Conway, 1941;Trump & Ginn, 1968;Okamoto & Quastel, 1970;Mazet, Claret & Claret, 1974;Cooke, 1975;Hughes & Macknight, 1977); and (3) decreases in swelling during metabolic blockade when sodium is replaced by a cation to which the cell membrane is less permeable (Hughes & Macknight, 1977). In experiments in which cell volume increases in an 'isotonic' medium, increases in cell water are accompanied by increases in cell monovalent cations and chloride so that the calculated osmolarity of the fluid gained is approximately equal to the osmolarity of the bathing medium (Mudge, 1951;Leaf, 1956;Macknight & Leaf, 1977).…”

“…Continued low membrane permeability to sodium may account for the absence of cell swelling in some tissues after ouabain or after metabolic blockade. Likewise, the more rapid swelling observed after complete ion for ion replacement of medium sodium by potassium than after metabolic blockade in a physiologic high sodium, low potassium medium (Cooke, 1975;Hughes & Macknight, 1977) may reflect a higher membrane permeability to the major extracellular cation in the former preparation.…”