The Journal of Membrane Biology

, Volume 194, Issue 3, pp 165–176

Regulation of Ion Fluxes, Cell Volume and Gap Junctional Coupling by cGMP in GFSHR-17 Granulosa Cells

Article

DOI: 10.1007/s00232-003-2033-9

Cite this article as:
Ngezahayo, A., Altmann, B. & Kolb, HA. J. Membrane Biol. (2003) 194: 165. doi:10.1007/s00232-003-2033-9

Abstract

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 (Gj) and cytoplasmic concentration of free Ca2+ ([Ca2+]i) in a rat granulosa cell line GFSHR-17. The voltage-dependent gating of Gj varied for different cell pairs. One population exhibited a bell-shape dependence of Gj on transjunctional voltage, which was strikingly similar to that of Cx43/Cx43 homotypic gap junction channels expressed in pairs of oocytes of Xenopuslaevis. 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.

Keywords

Granulosa cells Gap junctions Ca2+ Cell volume shrinkage cGMP Apoptosis 

Copyright information

© Springer-Verlag New York Inc. 2003

Authors and Affiliations

  1. 1.Institut für BiophysikUniversität Hannover, Herrenhäuserstr. 2, D-30419 HannoverGermany

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