Xenopus oocytes are metabolically and electrically coupled to their surrounding follicular cells through gap junctions formed by connexin 38 (cx38). The aim of this work was to determine the contribution of follicular cells to the apparent specific membrane-capacitance (Cma) of the oocyte and to test the effect of different gap-channel blockers on their functional coupling. Follicle Cma was measured in oocytes under voltage-clamp conditions by using a double ramp-pulse protocol.

Freshly-detached follicles from the ovary had Cma values of 14.0±1.0, n=74. When the external ovarian-epithelium was removed, either by collagenase treatment or manually, Cma significantly diminished and this reduction was morphologically related to the loss of follicular cells. A further Cma decrease was observed in oocytes after removing their vitelline envelope, which eliminates all the follicular cells. Besides, Cma values of freshly-detached follicles declined with time after separation and this reduction was again morphologically correlated to the loss of follicular cells. Finally, we tested in freshly-detached follicles the effect on Cma of several gap-channel blockers, such as octanol (1.5 mM), flufenamic acid (200 mM) or CO₂ and the effect of cx-38 antisense. All of them induced only a moderate reduction on both Cma (12 to 28%) and the K⁺-current elicited by adenosine in follicular cells (10 to 38%). By contrast, oocyte gap-hemichannels were almost fully blocked (>90%) by these blockers. These results indicate that functional follicular cell-oocyte coupling can be maintained with only a small fraction of open gap junctions. Supported by DGICYT grant BFU2006-04781 (Spain).