A Ca2+-activated potassium channel (BKCa) in Leydig cells is involved in testosterone production

SPINNLER K; SIEBERT S; MATZKIN ME; KUNZ L; CALANDRA RS; FRUNGIERI MB; MAYERHOFER A

Hamburgo, Alemania

Congreso; 22. Jahrestagung der Deutschen Gesellschaft für Andrologie; 2010

BACKGROUND & OBJECTIVES: Previously, we found that human ovarian granulosa cells express all major types of Ca2+-activated potassium channels (KCa), including BKCa, IK and SKs (Traut et al., RB&E, 2009), which were found to be involved in steroid production. Whether human testicular Leydig cells are also endowed with KCas is not known. We focussed on BKCa, because this  Ca2+-activated K+-channel can be manipulated, e.g. by a specific blocker, the red scorpion toxin iberiotoxin, which binds to the outer face with high affinity and selectively inhibits the current by decreasing both the probability of opening and the open time of the channel. METHODS: Human: Paraffin embedded sections of human testicular biopsies were studied by immunohistochemistry. RT-PCR was performed by using human testes samples from Leydig cells obtained by laser microdissection (LMD). Hamster: RT-PCR was performed from isolated Leydig cells. The release of testosterone was examined in supernatant of isolated and cultured Leydig cells by radioimmunoassay (RIA). Paraffin embedded testes sections were subjected to immunohistochemistry for BKCa. Real time PCR was performed to evaluate levels of StAR and of steroidogenic enzymes. RESULTS: Immunohistochemistry and RT-PCR of human and hamster testicular tissue showed the presence of of BKCa in Leydig cells. The role of this channel in testosterone production was analyzed in hamster. As expected, during a 3 h stimulation period hCG (100 mIU/ml) led to a significantly increased release of testosterone over basal levels. Importantly, the presence of iberiotoxin further significantly increased this stimulated testosterone production. The further increase was not associated with detectable changes in StAR, or main steroidogenic enzymes (p450SCC or 17bHSD), as shown by real time PCR. CONCLUSION: Our results indicate that a KCa is involved in the stimulated regulation of steroid production in Leydig cells in hamster and, possibly, also in man. It may represent a cellular mechanism how the LH/hCG induced testosterone production is inhibited. Experiments are under way to examine the mechanism of actions. We hypothesize that it may be related to changes in intracellular Ca2+ which is known to be increased as a consequence of LH/hCG action and/or the regulation of the membrane potential by BKCa.