Figure 7. Effect of FK506 on IP₃-induced Ca²⁺ release in permeabilized SH-SY5Y or permeabilized A7r5 cells.

A, SH-SY5Y permeabilization and Ca²⁺ uptake were as described in Fig. 1A. After reaching a stable steady-state level for Ca²⁺, either FK506 (10 μM) or ethanol (0.1 %) were added (first arrow), 5 min before administration of IP₃ (0.1 μM; second arrow). Two separate experiments out of more than 10 are superimposed. B, permeabilization and loading of A7r5 monolayers was as described in Methods. The non-mitochondrial Ca²⁺ stores, loaded to steady state with ⁴⁵Ca²⁺, released Ca²⁺ passively when incubated in efflux medium in the continuous presence of 0.1 % ethanol (○ and □) or 10 μM FK506 (• and ▪) for 10 min, at which time 1 μM IP₃ (○ and •) or 10 μM A23187 (□ and ▪) were added for 2 min, as indicated by the horizontal bar. Ca²⁺ release was plotted as the fractional loss, i.e. the amount of Ca²⁺ leaving the stores in 2 min divided by the total store Ca²⁺ content at that time. The result is the mean of three experiments.