Insights into the physiological role of the KATP channel in human endocrine ovarian cells – a target for drugs

Introduction: The ATP-sensitive potassium channel (KATP), consisting of pore-forming Kir 6.x subunits and sulfonylurea receptor (SUR) subunits, was previously described in rat ovary. We have subsequently identified the KATP subunits Kir 6.1 and SUR 2B in cultured human granulosa cells (GCs) from patients undergoing in-vitro-fertilization. Furthermore, in human ovary we found Kir 6.1 in follicular GCs and luteal cells by immunohistochemistry (submitted). Because KATP is targeted by commonly used classes of drugs, we have now started to examine its function in GCs.

Methods and results: Measurements of progesterone and estradiol production by GCs indicated that KATP is involved in sex steroid hormone production. Thus, progesterone production, stimulated by hCG (human chorionic gonadotropin), was significantly reduced by applying glibenclamide, a KATP inhibitor. Using gene arrays and RT-PCR, we also obtained hints of action of the KATP opener diazoxide, which decreased aromatase mRNA levels, as well as estradiol levels. In order to elucidate the site(s) of action, we attempted next to determine the localization of functional KATP in human GCs. Evidence from immunelectron microscopy, as well as functional studies using real-time fluorescence microscopy, excluded functional KATP channels at the mitochondrial membrane. Rather, KATP is present (Kir 6.1) and functional in the plasma membrane, as revealed in patch-clamp recordings and real-time fluorescence microscopy. These studies showed that glibenclamide depolarized the plasma membrane, implying a role of the KATP channel in generation of the plasma membrane potential of GCs.

Conclusion: KATP is presumably involved in sex steroid production via control of the membrane potential and further as yet unknown steps. The presence of KATP channels in human ovarian endocrine tissues might be clinically relevant regarding potential targeting by frequently used classes of drugs.

(DFG Graduiertenkolleg 333)