Fig. 4.
Gβγ inhibits release in a voltage-independent manner without altering the time course of release at the crayfish NMJ at 12 ± 1°C. Pulses are 5 Hz. [Gβγ]electrode, 4 μM. (a) Representative experiment. Similar results were obtained in three more experiments. Gβγ microinjection (first arrow) lowered m from 0.13 ± 0.02 in control (●) to 0.04 ± 0.01 (○). Its effect lasted for ≈10 min. Two consecutive injections (arrows) of Gβγ (10-min interval) reduced release for ≈20 min. (b) Total of 30,000 pulses, n = 4. Gβγ lowered m from 0.12 ± 0.03 in control (solid line) to 0.03 ± 0.01 (broken line) but did not change τD (Inset, 0.34 ± 0.04 ms in control and 0.33 ± 0.04 ms with Gβγ) or the minimal delay (0.6 ms in control and with Gβγ). (c) Gβγ microinjection to a PTX-treated terminal lowered m from a maximum of 0.19 to a minimum of 0.068 (64% inhibition) (a representative experiment is shown; similar results were obtained in two more experiments). (d) Total of 15,000 pulses, n = 3. First, PTX alone was applied [solid line, m = 0.16 ± 0.01, τD = 0. 70 ± 0.03 (Inset)]. Subsequent Gβγ microinjection (broken line) reduced m to 0.07 ± 0.01 but did not affect τD (Inset, τD = 0. 71 ± 0.02). (e) Gβγ-induced inhibition is voltage-independent. It was 44.9 ± 2.6% at PA of −0.5 μA, 45.7 ± 1.8% at −0.7 μA, and 45.3 ± 4.1% at −0.9 μA (n = 4). (f) Injection of Gβγ did not affect Ca2+ currents (solid line, control; broken line, Gβγ).