| Texto completo | |
| Autor(es): |
Costa, Roberta Ribeiro
;
Varanda, Wamberto Antônio
[2]
Número total de Autores: 2
|
| Tipo de documento: | Artigo Científico |
| Fonte: | JOURNAL OF PHYSIOLOGY-LONDON; v. 585, n. 2, p. 339-349, Dec. 2007. |
| Área do conhecimento: | Ciências Biológicas - Biofísica |
| Assunto(s): | Cálcio |
| Resumo | |
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) | |
| Processo FAPESP: | 04/08868-0 - Consolidação do Centro de Microscopia Funcional do Campus da USP/ Ribeirão Preto |
| Beneficiário: | Roy Edward Larson |
| Modalidade de apoio: | Auxílio à Pesquisa - Programa Equipamentos Multiusuários |
| Processo FAPESP: | 06/50954-7 - Correntes iônicas e receptores na fisiologia de células excitáveis e não excitáveis |
| Beneficiário: | Wamberto Antonio Varanda |
| Modalidade de apoio: | Auxílio à Pesquisa - Temático |