Gap junctional communication between granulosa cells seems to play a crucial role for follicular growth and atresia. Application of the double whole-cell patch-clamp- and ratiometric fura-2-techniques allowed a simultaneous measurement of gap junctional conductance (G j) and cytoplasmic concentration of free Ca2+ ([Ca2+]i) in a rat granulosa cell line GFSHR-17. The voltage-dependent gating of G j varied for different cell pairs. One population exhibited a bell-shape dependence of G j on transjunctional voltage, which was strikingly similar to that of Cx43/Cx43 homotypic gap junction channels expressed in pairs of oocytes of Xenopus laevis. Within 15–20 min, gap junctional uncoupling occurred spontaneously, which was preceded by a sustained increase of [Ca2+]i and accompanied by shrinkage of cellular volume. These responses to the whole-cell configuration were avoided by absence of extracellular Ca2+, blockage of K+ efflux, or addition of 8-bromoguanosine 3′,5′-cyclic monophosphate (8-Br-cGMP) to the pipette solution. Even in the absence of extracellular Ca2+ or blockage of K+ efflux, formation of whole-cell configuration generated a Ca2+ spike that could be suppressed by the presence of 8-Br-cGMP. We propose that intracellular cGMP regulates Ca2+ release from intracellular Ca2+ stores, which activates sustained Ca2+ influx, K+ efflux and cellular shrinkage. We discuss whether gap junctional conductance is directly affected by cGMP or by cellular shrinkage and whether gap junctional coupling and/or cell shrinkage is involved in the regulation of apoptotic/necrotic processes in granulosa cells.
The Journal of Membrane Biology – Springer Journals
Published: Sep 19, 2003
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