Respiration and cell volume of primary cultured cerebral astrocytes in media of various osmolarities.

Respiration and cell volume of cerebral astrocytes from primary culture were measured in media of various osmolarities. Respiration was measured in 3T3 fibroblasts under similar conditions. Uncoupled respiration and respiration independent of oxidative phosphorylation were obtained by adding dinitrophenol and oligomycin, respectively. In NaCl media, dinitrophenol-stimulated respiration was inhibited at low and high osmolarities. With increasing osmolarity from 363 to 1185 mOsm, oligomycin-insensitive respiration increased and became the predominant respiratory component. The same respiratory changes in response to altered osmolarity were observed in 3T3 fibroblasts. In astrocytes, the oligomycin-insensitive respiration also increased in hyperosmolar sodium acetate media but was unchanged with increasing osmolarity in choline chloride or sucrose media. The increase in oligomycin-insensitive respiration in hyperosmolar NaCl media was blocked by amiloride, an inhibitor of passive Na+ movement. In contrast to amiloride, ouabain, an inhibitor of Na+, K+-ATPase, inhibited a constant amount of respiration with increasing NaCl concentration. The relationship of astrocyte volume to osmolarity was the same in hyper-osmolar media containing NaCl or sucrose. Cell volumes were greater in hypo-osmolar NaCl than in sucrose media. Our results suggest the presence of a Na+-dependent respiratory component in primary cultured cerebral astrocytes in media of increased osmolarity. This respiratory component is not coupled to oxidative phosphorylation or a Na+-K+-ATPase. It may be important in the proposed physiologic role of the astrocyte in maintaining brain extracellular water content and electrolyte concentrations.