title: The Ca2+-activated, large conductance K+-channel (BKCa) is a player in the LH/hCG signaling cascade in testicular Leydig cells.
abstract: In Leydig cells, hormonal stimulation by LH/hCG entails increased intracellular Ca(2+) levels and steroid production, as well as hyperpolarization of the cell membrane. The large-conductance Ca(2+)-activated K(+)-channel (BK(Ca)) is activated by raised intracellular Ca(2+) and voltage and typically hyperpolarizes the cell membrane. Whether BK(Ca) is functionally involved in steroid production of Leydig cells is not known. In order to explore this point we first investigated the localization of BK(Ca) in human and hamster testes and then used a highly specific toxin, the BK(Ca) blocker iberiotoxin (IbTx), to experimentally dissect a role of BK(Ca). Immunohistochemistry and RT-PCR revealed that adult Leydig cells of both species are endowed with these channels. Ontogeny studies in hamsters indicated that BK(Ca) becomes strongly detectable in Leydig cells only after they acquire the ability to produce androgens. Using purified Leydig cells from adult hamsters, membrane potential changes in response to hCG were monitored. HCG hyperpolarized the cell membrane, which was prevented by the selective BK(Ca) blocker IbTx. Steroidogenic acute regulatory (StAR) mRNA expression and testosterone production were not affected by IbTx under basal conditions but markedly increased when hCG, in submaximal and maximal concentration or when db-cAMP was added to the incubation media. A blocker of K(V)4-channels, expressed by Leydig cells, namely phrixotoxin-2 (PhTx-2) was not effective. In summary, the data reveal BK(Ca) as a crucial part of the signaling cascade of LH/hCG in Leydig cells. The hyperpolarizing effect of BK(Ca) in the Leydig cell membrane appears to set in motion events limiting the production of testosterone evoked by stimulatory endocrine mechanisms.
authors.affiliation: Instituto de Biología y Medicina Experimental, Consejo Nacional de Investigaciones Científicas y Técnicas, Buenos Aires 1428, Argentina.
authors.forename: M E
authors.initials: ME
authors.lastname: Matzkin
authors.forename: S
authors.initials: S
authors.lastname: Lauf
authors.forename: K
authors.initials: K
authors.lastname: Spinnler
authors.forename: S P
authors.initials: SP
authors.lastname: Rossi
authors.forename: F M
authors.initials: FM
authors.lastname: Köhn
authors.forename: L
authors.initials: L
authors.lastname: Kunz
authors.forename: R S
authors.initials: RS
authors.lastname: Calandra
authors.forename: M B
authors.initials: MB
authors.lastname: Frungieri
authors.forename: A
authors.initials: A
authors.lastname: Mayerhofer
mesh_terms: D000818:Animals; D006063:Chorionic Gonadotropin / Q000378:metabolism*; D006224:Cricetinae; D005453:Fluorescence; D005786:Gene Expression Regulation / Q000187:drug effects; D006801:Humans; D051037:Large-Conductance Calcium-Activated Potassium Channel alpha Subunits / Q000378:metabolism*; D007985:Leydig Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D007986:Luteinizing Hormone / Q000378:metabolism*; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D008647:Mesocricetus; D010455:Peptides / Q000494:pharmacology; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D013739:Testosterone / Q000096:biosynthesis; D000098682:Steroidogenic Acute Regulatory Protein
chemical_list: D006063:Chorionic Gonadotropin; C494841:KCNMA1 protein, human; D051037:Large-Conductance Calcium-Activated Potassium Channel alpha Subunits; D010455:Peptides; D010750:Phosphoproteins; D012333:RNA, Messenger; D000098682:Steroidogenic Acute Regulatory Protein; D013739:Testosterone; C064719:iberiotoxin; D007986:Luteinizing Hormone