Increased Potassium Conductance in Rana Follicles after Stimulation by Pituitary Extract: (amphibian follicle/meiotic...

Pituitary gonadotropins are believed to induce the somatic cell portion of the amphibian follicle to synthesize and release progesterone which, in turn, induces the resumption of the meiotic divisions in the follicular oocyte. We report here that pituitary extract, at concentrations that induce ovulation and meiosis, causes a rapid hyperpolarization of the follicular oocyte. A similar hyperpolarization is seen in response to porcine LH but not FSH. Voltage clamp studies indicate that this is due to an increase in follicle K+ conductance. An electrical model of the amphibian follicle suggests that pituitary factors act by increasing the K+ conductance of the oolemma, by increasing the extent of oocyte-follicle cell ionic coupling, or by increasing the conductance of follicle cell plasma membrane. The conductance change does not occur in the absence of follicle cells, is not mediated by progesterone, and is not necessary for meiotic maturation, per se, but may play a role in processes which accompany or follow maturation.