Related Experiment Videos
Calcium-activated potassium channels are involved in the response of mouse Leydig cells to human chorionic
1Departamento de Fisiologia, Faculdade de Medicina de Ribeirão Preto, Universidade de São Paulo, Brasil.
Abstract:
The patch-clamp technique was used to investigate the involvement of ion channels in the response of Leydig cells to gonadotropic hormones (viz. hCG). Recordings in the cell-attached configuration (pipette containing 140 mM KCl) showed unitary events with conductance of 187.9 +/- 5.2 pS (N = 24 patches) in about 70% of the cells. These channels were potassium selective and the open channel probability (Po) was always about 1% for displacement of potential from the resting value in the range of -20 to +60 mV. Treatment of the cells with hCG (2 ng/ml) led to a large increase in the frequency of openings, concomitant with a reduction in the mean closed time and there was essentially no effect on the mean open time of the channel. Dibutyryl cAMP (100 microM) produced an effect similar to that of hCG and both required external calcium for their action. No direct effect of either dibutyryl cAMP or hCG were observed in inside-out patches. Reversal potential measurements on excised inside-out patches demonstrated that the channels were highly potassium selective with unitary conductance of about 206.8 +/- 6.36 pS (mean +/- SEM of 6 measurements), and an estimated permeability of 3.6 x 10(-13) +/- 0.2 x 10(-13) cm3/s (mean +/- SEM for 6 measurements), in symmetrical 140 mM KCl. The activity of the channel in excised patches was very sensitive to the free-calcium concentration on the intracellular surface of the channel. Po evaluated at +60 mV increased from 3% at 10 nM to 47% at 100 nM free calcium. The Hill coefficient under these conditions was 1.1. These results demonstrate that Leydig cells have a Ca2(+)-activated K+ channel of large unitary conductance, which can be activated upon the binding of hCG to receptors in the cell membrane.
Insights
Leydig cells possess a calcium-activated potassium channel that responds to human chorionic gonadotropin (hCG). This ion channel
Area of Science:
- Endocrinology
- Cell Physiology
- Ion Channel Biology
Background:
- Leydig cells are crucial for testosterone production, regulated by gonadotropic hormones like hCG.
- The precise ion channel mechanisms underlying Leydig cell responses to hCG are not fully understood.
Purpose of the Study:
- To investigate the role of ion channels in Leydig cell responses to hCG.
- To characterize the properties of ion channels modulated by hCG signaling.
Main Methods:
- Patch-clamp electrophysiology in cell-attached and inside-out configurations.
- Stimulation with hCG and dibutyryl cAMP.
- Measurement of unitary channel conductance, selectivity, and open channel probability (Po).
- Assessment of calcium sensitivity and reversal potential.
Main Results:
- A large conductance (approx. 188-207 pS), potassium-selective channel was identified in Leydig cells.
- hCG and dibutyryl cAMP increased channel opening frequency and decreased mean closed time, requiring external calcium.
- Channel activity was highly sensitive to intracellular calcium concentration, with Po increasing significantly from 10 nM to 100 nM free calcium.
- The channel exhibited properties consistent with a Ca2(+)-activated K+ channel.
Conclusions:
- Leydig cells express a Ca2(+)-activated K+ channel with large unitary conductance.
- This channel is activated by hCG, likely mediated through cAMP and intracellular calcium.
- The findings elucidate a novel ion channel mechanism involved in Leydig cell function and hormonal regulation.