An increase in intracellular calcium concentration Effects of osmotic perturbation on [Ca2+]i and pHi in rabbit ([Ca2+Ji) could play a role in the process of regulatory proximal tubular cells in primary culture. Am. J. Physiol. 269 volume decrease (RVD) observed after osmotic cell (Renal Fluid Electrolyte Physiol. 38): F205-F211, 1995. The effects of anisosmotic media on intracellular Ca2+ and H + swelling (19). Such an increase in [Ca2+]j could activate K+ and Cl" channels, which results in

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... efflux concentrations i[Ca*+|, and pH" respectively) were studied to foUowec| by water and restoration of cell volume. In PT investigate whether these changes play a role in epithelial cell cel]s 0f the rabbit, an increase in [Ca121 j after cell volume regulation. C a n and pH, were measured in rabbit sweUing haa been reported (3,18, 19, 31) . In contrast to proximal tubular cells in primary culture using the fluorescent ^ m u ititu d e of studies deaH ^ osm otic swelling, ratio probes fura 2 and 2\7'-bis(carboxyethyl)-5(6)-carboxyfluorescein. Changing medium osmolarity from 300 to 150 mosmol resulted in a rapid transient increase in fura 2 ratio from 0.89 ± 0.02 to 1.15 ± 0.03, which lasted for several minutes and returned to base line within 10 min. The source of Ca2+ few reports on cell shrinkage or regulatory volume increase (RVI) and [Ca2H ]i are studied. Because changes in [Ca2+]; and intracellular pH (pHj) are often interre lated, we studied both [Ca2'^ and pHj during osmotic was extracellular as well as intracellular. Simultaneous with p ertu rb a tio n of P T cells in prim ary culture. this increase in [Ca2+li, cells slowly acidified from pH; of 7.51 0.03 to 6.86 ± 0.02. This osmotic swelling-induced acidifica tion could not be explained by a decrease in the rate of Na+/H +