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

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 (Mg2+) or manganese (Mn2+) associate with ATP to form the real substrates of ACs. In addition, ACs are sensitive to calcium (Ca2+) but in a different way than Mg2+ or Mn2+. Indeed, LH increases the cytoplasmic calcium ion concentration ([Ca2+]cyt) but only when Ca2+ is present in the extracellular medium. Materials and Methods: In the present study, the effects of intracytoplasmic Ca2+, Mg2+, 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 Ca2+, 5 μM Mg2+, or 5 μM Mn2+. The intracellular cyclic AMP accumulation was then monitored under LH stimulation. Results: Our findings revealed that only Mg2+ and Mn2+ in the extracellular medium potentiate the cAMP response to hLH, in contrast to Ca2+. In addition, we also showed that HCO3- increased the stimulation of the adenylyl cyclase enzyme by Ca2+, Mg2+ or Mn2+. Conclusions: In mLTC-1 cells, extracellular Mg2+ and Mn2+ might potentiate LH-stimulated ACs activity by favoring LH interaction with its receptor, whereas Ca2+ from internal stores might be mobilized towards the cytoplasm to increase ACs activity, possibly through the soluble isoform.