Figure 2. Dependence of astrocyte calcium changes on NH₄ ⁺/NH₃-concentrations.

(A) Calcium changes in an hippocampal astrocyte evoked by stepwise increases in the NH₄ ⁺/NH₃ concentration by 0.5 mM for 2 minutes, starting from nominally 0 mM up to a final concentration of 5 mM which was then maintained for another 15 minutes. (B) Influence of methioninesulfoximine (MSO, 100 µM) on NH₄ ⁺/NH₃-induced calcium changes in a hippocampal astrocyte. The grey bar indicates the average amplitude of the sustained calcium increase evoked under control conditions in the absence of MSO (∼50 nM). (C) Histogram showing the mean peak amplitude ± S. E. M. of sustained calcium changes in response to 1, 2 and 5 mM NH₄ ⁺/NH₃, after stepwise increases from 0 to 5 mM NH₄ ⁺/NH₃ and in the presence of MSO and 5 mM NH₄ ⁺/NH₃. The number of cells is given within the bars. Peak amplitudes of calcium changes did not differ between the different concentrations used. They were, however, significantly larger in the presence of MSO as compared to all other conditions (*: p<0.05; **: p<0.01).