Luteinizing hormone (LH) regulates testosterone synthesis in Leydig cells by inducing an intracellular increase in cAMP concentration. LH also increases the intracellular calcium concentration ([Ca2+]i), dependent on the presence of Ca2+ in the extracellular medium ([Ca2+]e) for its effect. Despite these evidences, the identity of a pathway for calcium entry has remained elusive and the relationship between cAMP and [Ca2+]i has been questioned. Here we show that mice Leydig cells do have an inward Ca2+ current carried by T-type Ca2+ channels. In 10 mm [Ca2+]e, the currents start to be activated at −60 mV, reaching maximal amplitude of 1.8 ± 0.3 pA pF−1 at −20 mV. Currents were not modified by Ba2+ or Sr2+, were suppressed in Ca2+-free external solution, and were blocked by 100 μm nickel or 100 μm cadmium. The Ki for Ni2+ is 2.6 μm and concentrations of Cd2+ smaller than 50 μm have a very small effect on the currents. The calcium currents displayed a window centred at −40 mV. The half-voltage (V0.5) of activation is −30.3 mV, whereas the half-voltage steady-state inactivation is −51.1 mV. The deactivation time constant (τdeactivation) is around 3 ms at −35 mV. Confocal microscopy experiments with Fluo-3 loaded cells reveal that both LH and dibutyryl-cAMP (db-cAMP) increase [Ca2+]i. The db-cAMP induced calcium increase was dependent on Ca2+ influx since it was abolished by removal of extracellular Ca2+ and by 400 μm Ni2+. [Ca2+]i increases in regions close to the plasma membrane and in the cell nucleus. Similar effects are seen when Leydig cells are depolarized by withdrawing K+ from the extracellular solution. Altogether, our studies show that Ca2+ influx through T-type Ca2+ channels in the plasma membrane of Leydig cells plays a crucial role in the intracellular calcium concentration changes that follow binding of LH to its receptor
To submit an update or takedown request for this paper, please submit an Update/Correction/Removal Request.