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1 Physiology and Pharmacology, The University of Western Ontario, London, Ontario, Canada; Obstetrics and Gynaecology, The University of Western Ontario, London, Ontario, Canada
2 Physiology and Pharmacology, The University of Western Ontario, London, Ontario, Canada; Obstetrics and Gynaecology, The University of Western Ontario, London, Ontario, Canada; 800 Commissioners Road East, Children's Health Research Institute, London, Ontario, Canada
3 Physiology and Pharmacology, The University of Western Ontario, London, Ontario, Canada
* To whom correspondence should be addressed. E-mail: donglin.bai{at}fmd.uwo.ca.
Genetic ablation of connexin37 (Cx37) or connexin43 (Cx43), the two gap junction proteins expressed by mouse ovarian granulosa cells, has been shown to result in impaired follicle development. We used patch clamp techniques to evaluate quantitatively the contribution of these connexins to gap junctional intercellular communication (GJIC) among granulosa cells. The coupling conductance derived from a voltage step-induced capacitive current transient was used as a measure of GJIC in cultured granulosa cells. Using this method, we determined that the conductance of wildtype (84.1 ± 28.6nS, n=6) and Cx37-deficient (83.7 ± 6.4nS, n=11) granulosa cells does not differ significantly (P=0.35), suggesting a very limited contribution, if any, of Cx37 to granulosa cell coupling. In contrast, the conductance between the granulosa cells of Cx43-deficient mice (2.6 ± 0.8nS, n=5) was not significantly different from that of single isolated wildtype granulosa cells (2.5 ± 0.7nS, n=5; P=0.83), indicating that Cx43-deficient granulosa cells are not electrically coupled. A direct measurement of transjunctional conductance between isolated granulosa cell pairs by dual patch clamp confirmed this conclusion. Interestingly, a partial rescue of folliculogenesis was observed when the Cx43 null mutation from C57BL/6 mice was crossed into the CD1 strain and capacitive current measurement demonstrated that this rescue was not due to re-establishment of gap junctional communication. These results demonstrate that folliculogenesis is impaired in the absence of gap junctional communication between granulosa cells, but they also indicate that the severity is genetic background dependent, a phenomenon that cannot be attributed to the expression of additional connexins.
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