Fig. 4

A An example of [Mg²⁺]_i measurements in which Mg²⁺ efflux was induced by 140 mM extracellular Na⁺ with simultaneous application of 30 µM KB-R7943 at the time indicated by the arrow (25°C). B The onset of the inhibitory effect of KB-R7943 obtained from the experiments of the type shown in A. KB-R7943 (30 µM) was applied simultaneously with 140 mM Na⁺ to the Mg²⁺-loaded cells at time zero on the abscissa, and the values of relative Δ[Mg²⁺]_i/Δt were plotted as a function of time after application of the drug. The first point at 60 s was obtained by linear regression of [Mg²⁺]_i data between 30 and 90 s after application of KB-R7943, and the following points were similarly obtained with 60-s intervals. Each symbol represents a mean value from 3 cells. A solid line was drawn by nonlinear least-squares fitting with an exponential (plus constant) function of the form and values as indicated in the graph