Fig. 5.

Sodium dependence of forskolin action on Ca²⁺ influx in rat anterior pituitary cells. A: stimulation of Ca²⁺ influx by 5 μM forskolin in cells bathed in 50 μM tetrodotoxin (TTX). Gray arrows indicate the moment of TTX application (top 3 traces). In some experiments, TTX was applied for 15 min prior to forskolin application (bottom 2 traces). B: the lack of effects of rilusole, a blocker of leak Na⁺ channels, on forskolin-stimulated Ca²⁺ influx. C: inhibition of spontaneous Ca²⁺ influx by replacing bath Na⁺ with N-methyl-d-glucamine (NMDG⁺). Notice the lack of effect of forskolin in cells bathed in NMDG⁺-containing medium. Traces shown are representative from 4 (A), 4 (B), and 3 experiments (C) with ≥15 recordings/experiment.