Role of Intracellular Divalent Cations on the Adenylate Cyclase Activation by Human LH in mLTC-1 Leydig Cells

Introduction: the luteinizing hormone (lh) regulates leydig cell activities through lhr occupation, promoting gs protein and/or β-arrestin activation. the activated gsαgtp subunit stimulates adenylyl cyclase (acs) and, therefore, intracellular cyclic adenosine monophosphate (camp) accumulation from the ac substrate adenosine triphosphate (atp). the divalent cations, magnesium (mg^2+) or manganese (mn^2+) associate with atp to form the real substrates of acs. in addition, acs are sensitive to calcium (ca^2+) but in a different way than mg^2+ or mn^2+. indeed, lh increases the cytoplasmic calcium ion concentration ([ca^2+]cyt) but only when ca2+ is present in the extracellular medium.materials and methods: in the present study, the effects of intracytoplasmic ca^2+, mg^2+, and mn2+ on the cyclic amp response to human lh in mltc^-1 leydig tumor cells were investigated. the mltc^-1 cells were incubated at 37 °c in media supplemented with and without 5 μm ca^2+, 5 μm mg^2+, or 5 μm mn^2+. the intracellular cyclic amp accumulation was then monitored under lh stimulation.results: our findings revealed that only mg^2+ and mn2+ in the extracellular medium potentiate the camp response to hlh, in contrast to ca^2+. in addition, we also showed that hco3- increased the stimulation of the adenylyl cyclase enzyme by ca^2+, mg^2+ or mn^2+.conclusions: in mltc^-1 cells, extracellular mg2+ and mn2+ might potentiate lh-stimulated acs activity by favoring lh interaction with its receptor, whereas ca^2+ from internal stores might be mobilized towards the cytoplasm to increase acs activity, possibly through the soluble isoform.