Figure 5.

Relationship between the degree of dissociation of ANK220 from IP₃R-3 induced by Sig-1R ligands and the Sig-1R ligands' abilities to potentiate bradykinin-induced increase in [Ca^{2 +} ]cyt in NG-108 cells. (A) Potentiation of the bradykinin-induced increase in [Ca²⁺]cyt by (+)PTZ (100 nM, 10 min). (B) Temporal correlation of (+)PTZ (100 nM) in increasing the dissociation of ANK220 from IP₃R-3 and in potentiating the [Ca²⁺]cyt increase induced by bradykinin. The numbers below open circles indicate the treatment time (min) of NG-108 cells with (+)PTZ. (C) Efficacy correlation of Sig-1R ligands in their abilities to cause ANK220 dissociation from IP₃R-3 at the 10-min point and in their abilities at the same time point to potentiate bradykinin-induced increases in [Ca²⁺]cyt. Concentrations of Sig-1R ligands were all 100 nM. The total number of cells examined and the number of determinations (in parentheses) for each test drug are indicated (see Methods): NE-100, 23 cells (5); pregnenolone sulfate, 58 cells (7); progesterone, 34 cells (5); PRE084, 91 cells (14); (+)SKF-10047, 36 cells (6); (+)PTZ, 59 cells (8). The value on the x axis represents the mean value from all determinations for each drug. (D) Increase in [³H]IP₃ binding to microsomes of NG-108 cells caused by (+)PTZ. After the (+)PTZ treatment (100 nM, 10 min), cells were harvested and P3 fractions prepared and used for [³H]IP₃ binding assay. Data represent mean ± SEM of three determinations, each assayed in triplicate. *, P < 0.05.