Figure 2. Effects in cultured granule (CG) neurons of thiopental and methohexital on intracellular [Ca²⁺]([Ca²⁺]ⁱ) transients elicited by a depolarization induced by sudden increase in [K⁺] from 5 to 55 mM at time zero. [Ca²⁺]ⁱwas determined by the excitation fluorescence ratio method in cells that had been loaded with fura-2. Transients are shown for neurons on different coverslips from the same batch of cultured neurons on the same day. Responses are shown for control and in the presence of different concentrations of thiopental (A) or methohexital (B). (C) Dose dependence of decrease in the peak [Ca²⁺] transient by either thiopental (filled circles) or by methohexital (open circles). Each point represents a determination expressed as a fraction of the control measurement(s) made the same day. The lines represent a least-squares fit to the standard logistic equation: Fraction of control = 1/(1 +([drug]/IC⁵⁰)ⁿ), with an IC⁵⁰(mean +/- SEM) for thiopental of 36 +/- 5 [micro sign]M and slope factor n (mean +/- SEM) of 0.85 +/- 0.15. For methohexital, the IC⁵⁰value was 9.6 +/- 2.0 [micro sign]M, with n of 0.63 +/- 0.15.