Role of Intracellular Divalent Cations on the Adenylate Cyclase Activation by Human LH in mLTC-۱ 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 (Mg۲+) or manganese (Mn۲+) associate with ATP to form the real substrates of ACs. In addition, ACs are sensitive to calcium (Ca۲+) but in a different way than Mg۲+ or Mn۲+. Indeed, LH increases the cytoplasmic calcium ion concentration ([Ca۲+]cyt) but only when Ca۲+ is present in the extracellular medium.Materials and Methods: In the present study, the effects of intracytoplasmic Ca۲+, Mg۲+, and Mn۲+ on the cyclic AMP response to human LH in mLTC-۱ Leydig tumor cells were investigated. The mLTC-۱ cells were incubated at ۳۷ °C in media supplemented with and without ۵ µM Ca۲+, ۵ µM Mg۲+, or ۵ µM Mn۲+. The intracellular cyclic AMP accumulation was then monitored under LH stimulation.Results: Our findings revealed that only Mg۲+ and Mn۲+ in the extracellular medium potentiate the cAMP response to hLH, in contrast to Ca۲+. In addition, we also showed that HCO۳- increased the stimulation of the adenylyl cyclase enzyme by Ca۲+, Mg۲+ or Mn۲+.Conclusions: In mLTC-۱ cells, extracellular Mg۲+ and Mn۲+ might potentiate LH-stimulated ACs activity by favoring LH interaction with its receptor, whereas Ca۲+ from internal stores might be mobilized towards the cytoplasm to increase ACs activity, possibly through the soluble isoform. 

Keywords:

Adenosine Monophosphate , Adenylyl Cyclase , mLTC-۱ , luteinizing hormone , Forskolin