Calcium and voltage-dependent alterations of cell volume in neuroblastoma×glioma hybrid NG108-15 cells

Intracellular calcium ([Ca2+]i), cell volume, membrane potential and currents were measured in neuroblastoma×glioma hybrid cells to gain insight into how [Ca2+]i controls cell volume. [Ca2+]i was increased by fluid shear stress, mechanical stimulation of the cells, the Ca2+ ionophore A23187, caffeine and thapsigargin. The increase in [Ca2+]i induced by mechanical stimulation was decreased by about 50% by caffeine and abolished after incubation of the cells in a Ca2+-free solution. Mechanical stimulation by stirring the cell suspension induced cell shrinkage that was abolished by caffeine, but induced cell swelling in Ca2+-free solution. In the presence of caffeine, A23187 induced cell shrinkage whereas thapsigargin induced cell swelling. Both cell volume changes were inhibited by the Cl– channel blocker 5-nitro-2-(3-phenylpropylamino) benzoic acid. The cells were hyperpolarized by fluid shear stress and A23187 and depolarized by caffeine, thapsigargin and intracellular EGTA. Under all these conditions, the membrane input resistance was decreased. Voltage-clamp experiments suggested that, in addition to an increased anionic current, fluid shear stress and A23187 increased a K+ current, whereas caffeine and intracellular Ca2+ chelation increased a non-selective cation current and thapsigargin increased both a K+ and a non-selective cation current. Taken together, these results suggest that, if cell volume is closely dependent on [Ca2+]i and the activity of Cl– channels, its relative value is dependent on the ionic selectivity of co-activated channels and the membrane potential.