| Full text | |
| Author(s): |
Costa, Roberta Ribeiro
;
Varanda, Wamberto Antônio
[2]
Total Authors: 2
|
| Document type: | Journal article |
| Source: | JOURNAL OF PHYSIOLOGY-LONDON; v. 585, n. 2, p. 339-349, Dec. 2007. |
| Field of knowledge: | Biological Sciences - Biophysics |
| Abstract | |
Luteinizing hormone (LH) regulates testosterone synthesis in Leydig cells by inducing an intracellular increase in cAMP concentration. LH also increases the intracellular calcium concentration ([Ca(2+)](i)), dependent on the presence of Ca(2+) in the extracellular medium ([Ca(2+)](e)) for its effect. Despite these evidences, the identity of a pathway for calcium entry has remained elusive and the relationship between cAMP and [Ca(2+)](i) has been questioned. Here we show that mice Leydig cells do have an inward Ca(2+) current carried by T-type Ca(2+) channels. In 10 mM [Ca(2+)](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 Ba(2+) or Sr(2+), were suppressed in Ca(2+)-free external solution, and were blocked by 100 mu m nickel or 100 mu m cadmium. The K(i) for Ni(2+) is 2.6 mu M and concentrations of Cd(2+) smaller than 50 mu m have a very small effect on the currents. The calcium currents displayed a window centred at -40 mV. The half-voltage (V(0.5)) of activation is -30.3 mV, whereas the half-voltage steady-state inactivation is -51.1 mV. The deactivation time constant (tau(deactivation)) 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 [Ca(2+)](i). The db-cAMP induced calcium increase was dependent on Ca(2+) influx since it was abolished by removal of extracellular Ca(2+) and by 400 mu M Ni(2+). [Ca(2+)](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 Ca(2+) influx through T-type Ca(2+) 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. (AU) | |
| FAPESP's process: | 06/50954-7 - Ionic currents and receptors in the physiology of excitable and non-excitable cells |
| Grantee: | Wamberto Antonio Varanda |
| Support Opportunities: | Research Projects - Thematic Grants |