Fluid compartmentation and electrolytes of cat cerebral cortex in vitro. II. Sodium, potassium and chloride of mature cerebral cortex.

Abstract

SUMMARYThe contents of K+, Na+ and Cl− in various incubation media and in slices of adult cat cerebral cortex incubated in vitro under a variety of conditions have been determined in conjunction with studies on slice swelling and fluid compartmentation reported in the preceding paper (Bourke and Tower, 1966).Cortical slices incubated in media containing 16 Or 27 mm‐K+ exhibit contents of K+ and Na+ most nearly comparable to those found in viuo. Substitution of isethionate− For Cl− or omission of Ca2+ in such media have little effect on slice cation composition. Rb+ can effectively substitute for K+, but substitution of Li+ or choline+ for most of the naf in incubation media is associated with accumulation of these cations in slices at the expense of both K+ and Na+.Compared to values in vivo for net contents and/or concentrations of electrolytes in the non‐sucrose spaces of cortical slices, conditions yielding most favourable data in vitro appeared to be incubation of cortical slices in 16 mm‐K+ medium or in 27 mm‐K+ medium with either omission of Ca2+ or replacement of Cl− by isethionate.Essentially complete inhibition of maintenance of K+ and extrusion of Na+ in slices of cat cerebral cortex occurs upon incubation with 10−5 or 10−4m‐ouabain, with 50 per cent inhibition of cortical slice electrolyte metabolism occurring at about 8 × 10−7m‐ouabain.Cortical slices incubated in 27 mm‐K+ medium in the presence of 42K exhibited rates of exchange and turnover of slice K+ (in non‐sucrose spaces) of 0·7 μequiv./min and 6.45 per cent respectively. In the presence of 10−5m‐ouabain, a maximal ratio of slice specific activity/medium specific activity is attained within about 5 min after 42K addition, compared to >20 min for control slices. In neither case does the maximal specific activity ratio exceed about 0.85; this suggests that some 10‐15 per cent of total cortical K+ comprises a “slowly exchangeable” fraction.In the presence of Ca2+ (1.3 mm) slice oxygen consumption is markedly stimulated (39 per cent) and aerobic glycolysis is markedly depressed (54 per cent) in the presence of 10−5m‐ouabain; whereas on omission of Ca2+ from incubation media, both respiration and glycolysis are normally stimulated but, with 10−5m‐ouabain present, both are significantly depressed (20 per cent and 37 per cent respectively). Possible relevance of these effects to mobilization of tissue Ca2+ by ouabain and to effects of intracellular Ca2+ on mitochondrial respiratory metabolism is discussed.