Exp Clin Endocrinol Diabetes 2007; 115 - P01_003
DOI: 10.1055/s-2007-972259

Characterization of the KATP channel in human granulosa cells: Electrophysiology and regulation

JS Richter 1, L Kunz 1, D Berg 2, U Berg 2, A Mayerhofer 1
  • 1Anatomisches Institut der LMU am Biederstein, München, Germany
  • 2IVF-Labor A.R.T. Bogenhausen, München, Germany

Objectives: We recently identified an ATP-sensitive potassium channel (KATP), Kir 6.1/SUR 2B, in the human ovary and in cultured human granulosa cells (GC). It is localized in the plasma membrane of human GC and is involved in the generation of the plasma membrane potential and in steroidogenesis (JCEM. 2006; 91:1950–5). We now further characterized the ovarian KATP and attempted to elucidate how it is linked to the reduction of steroid production.

Results: Single-channel measurements revealed distinct characteristics of the GC KATP, including inward rectification, a conductance of about 44 pS and regulation by the ATP/ADP ratio. The KATP is inhibited by glibenclamide, as whole-cell patch-clamp experiments indicated. Kir 6.1 and SUR 2B are present in the follicle and the young and old Corpus luteum of human and monkey ovary, as shown by RT-PCR and immunohistochemistry, implying physiological relevance. Sequencing of monkey Kir 6.1 and SUR 2B subunits showed differences compared to the human sequence that would lead to the substitution of one amino acid in Kir 6.1 and two amino acids in SUR 2B. Furthermore, both subunits in GC were not affected by LH/hCG (24h), as indicated by semiquantitative RT-PCR and WB experiments. As inhibition of the KATP by glibenclamide reduces the progesterone production of human GC, we examined whether KATP modulators affect mRNA levels of crucial enzymes of steroidogenesis, including StAR, SCC and 3β-HSD. Results obtained did not show any changes in mRNA levels of these enzymes. Thus, they are probably not involved in the reduction of the hCG-induced progesterone production by glibenclamide.

Conclusion: In summary, the KATP of human GC shows typical electrophysiological properties, is not affected by the trophic hormone LH/hCG and is not directly connected to the expression of typical steroidogenic pathway enzymes. The mechanism of modulation of steroid production remains to be shown, a task of interest regarding the possibility that antidiabetic drugs like glibenclamide could thus influence ovarian function.

(DFG Graduate School 333)