Cell water content was measured in respiring rat renal cortical slices incubated in hypo- and hyperosmolal saline with and without raffinose and ouabain for 60 min at 37 degrees C. At 60 min, hyposmolal saline (228 mosmol/kg H2O) caused a 16% swelling of cells, whereas addition of 73 mM raffinose (299 mosmol/kg H2O) caused a 33% shrinkage. Physiological saline plus raffinose (364 mosmol/kg H2O) caused a 28% cell shrinkage, whereas addition of saline (385 mosmol/kg H2O) produced only a 10% decrease in cell volume. The effects of raffinose were reversible. At physiological Na concentrations, osmole for osmole raffinose was 4 times as effective in shrinking cells as saline, but only 2 times as effective at Na of 112 mM. Osmotic effectiveness of saline changed, that of raffinose did not. Ouabain caused no changes in cell volume and did not prevent the effect of raffinose. In conclusion, there is no volume regulation to nonelectrolyte solutes and only partial volume regulation to saline, and this is due to differential osmotic effects of these solutes, that of saline decreasing from low to high Na.

Summary. Changes in cell Na, K and Cl content (per kg dry weight) and concentration (per kg intracellular water) were measured in respiring rat renal cortical slices incubated for 60 min at 37° in hypo-and hypertonic saline with and without the addition of a non-electrolyte (raffinose). Both hypertonic saline and raffinose increased cellular concentration of Na, Cl and K, the former by producing minimal cell shrinkage and major entry of Na and Cl into the cell, the latter entirely by cell shrinkage leading also to a loss of Na content but not of K. In hypotonic saline both content and concentration of Na and Cl did not change significantly, whereas that for K dropped markedly. Addition of ouabain (1 mmoI/1) produced a significant gain of cell Na and loss of K on a one to one basis but did not alter the effect of raffinose. It is concluded that sustained changes in cell ion concentrations and content in response to pericellular osmolality are produced and that these are directed towards equilibrating cellular activity of water to that of the surrounding medium.

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1. In vivo micropuncture techniques, with and without peritubular capillary perfusion, were used to study the effects of high extracellular Na and Cl concentrations on transepithelial volume (Jv) and sodium (JNa) fluxes in rat proximal tubules. 2. In a double blind manner, the shrinking drop technique of Gertz was used to measure Jv; JNa was calculated from this and the tubular fluid Na concentration. 3. At both 184 and 279 mmol/l pericellular Na concentrations (both inside and outside the tubular epithelium), net Jv decreased significantly by 15 and 64%, respectively. Net JNa remained constant at 184 but decreased by 29% at 279 mmol/l Na concentration. 4. Thus, at both Na concentrations, when translated to free flow conditions, fractional Na reabsorption must have decreased. These findings, also supported by previous results at these Na concentrations, indicate that active Na transport was inhibited by high pericellular Na concentrations. 5. When intratubular Cl concentration was varied between 108 and 138 mmol/l while peritubular Cl was maintained constant (blood perfusing the capillaries), neither Jv nor JNa changed. Thus, at zero tubular flow, differential Cl/HCO3 concentrations do not provide significant driving forces for net Jv or JNa. 6. When only intratubular but not peritubular Na was elevated to 279 mmol/l, Jv and JNa increased markedly by 50 and 187%, providing evidence that a true solvent drag (solute drag) effect does exist in rat proximal tubules. 7. These findings offer a mechanism to explain why Na reabsorption is not increased when the filtered load of Na is increased with an elevation of plasma Na.(ABSTRACT TRUNCATED AT 250 WORDS)