Fig. 1. LH reduces gap junction permeability between cumulus and mural granulosa cells. Determined by injecting Alexa Fluor 350 into the oocyte and imaging its diffusion within the follicle at 20 minutes after injection. (A,B) No LH. (C,D) LH applied 70 minutes before injecting Alexa Fluor 350. Upper panels show scanning transmission images; lower panels show Alexa Fluor 350 distribution. In A and B, Alexa Fluor 350 diffused throughout the mural granulosa cells, whereas in C and D, the Alexa Fluor 350 spread into the cumulus cells, but little or none was seen in the mural granulosa cells. (E) Regions of the follicle used for the measurements shown in F. The dashed lines indicate the approximate border between the cumulus mass and the antral space. (F) Ratio of fluorescence intensity in the mural granulosa cells to that in the inner cumulus cells, as a function of LH treatment time. Measurements were made at 20 minutes after injecting Alexa Fluor 350 into the oocyte. Bars show mean±s.e.m., and the numbers in parentheses indicate the number of follicles tested at each time point (0.5 hour=33-40 minutes, 1 hour=64-75 minutes, 2 hours=124-140 minutes, 5 hours=4.5-5.7 hours).