Figure 1. Current-voltage and dose-response relationships of follicular responses generated by ACh.

A, membrane current-voltage relationships of F_in (•) and I_K,cAMP (▴) elicited by FSH (0.25 μg ml⁻¹), and during I_K,cAMP inhibition (○) by 0.1 μm ACh. Each point indicates the mean (±s.e.m.) from 4-7 follicles (3 frogs) tested in each condition. Reversal potentials for the currents were -21.6 ± 3, -98 ± 2 and -55 ± 9 mV, respectively. B, top traces: follicular F_in elicited by ACh applied consecutively at concentrations of 0, 0.05, 0.1, 0.5, 1 and 10 μm, with 10 min wash intervals in NR solution. The ACh applications started at the point indicated by the arrow and lasted about 80 s. The superimposed traces are from a single epithelium-removed follicle held at -60 mV. Bottom, 10 μm ACh application in a defolliculated oocyte from the same frog. C, top traces: inhibition of I_K,cAMP (generated by FSH) by increasing concentrations of ACh (0, 1, 5, 10, 50 and 100 nm, with 15 min wash intervals). Data from 1 follicle held at -40 mV. In this and subsequent records, the bars indicate the time of drug application, and voltage steps of +20 mV (2 s) were applied periodically to monitor membrane conductance. Bottom, FSH application in a defolliculated oocyte from the same frog. D, dose-response relationships for activation of F_in (•) and inhibition of I_K,cAMP (○) normalized with respect to the maximal response. Means (±s.e.m.) of 12-16 follicles from 5 frogs. Curves are fits to the equation:

by the method of non-linear least squares fitting, where EC₅₀ is the half-maximal effective concentration of ACh, n_H is the slope factor (Hill coefficient), A₁ and A₂ are the initial and final normalized I values, respectively, and [ACh] is the concentration of the neurotransmitter.