Potassium and chloride conductances in rat Leydig cells: effects of gonadotrophins and cyclic adenosine monophosphate.

Abstract

SUMMARY1. The effects of gonadotrophins (luteinizing hormone and human chorionic gonadotrophin) and cyclic AMP on ionic conductances were investigated using the tight-seal whole-cell recording technique in Leydig cells freshly isolated from nature rat testis by enzymatic treatment.2. In resting cells, the predominant ionic conductance is a voltage-dependent K+ conductance resembling the delayed rectifier K+ conductance of T-lymphocytes. This conductance is characterized by: (1) a time-dependent inactivation for potentials more positive than +20 mV, (2) a reversal potential near -65 mV, (3) a sensitivity to intracellular Cs+, and (4) a sensitivity to extracellular TEA and 4-aminopyridine.3. A Cl-conductance is also present resembling the Cl-background conductance in squid axons and heart cells. In resting cells, this conductance contributes only a small component of the total outward current obtained with depolarizing pulses.4. Gonadotrophins (human chorionic gonadotrophin, porcine luteinizing hormone and ovine luteinizing hormone) have little effect on the K+ conductance. They transiently increase a Cl-conductance after a delay of up to 30 s. This response does not occur if the hormones are applied late in the whole-cell recording. Gonadoliberine (GnRH) does not affect the Cl-or K+ conductance.5. Internal cyclic AMP (100 /IM) mimics all these effects while internal application of a GTP-ATP mixture induces a similar response, which is, however, sustained rather than transient.6. The Cl-conductance was studied quantitatively with a GTP-ATP internal solution. This conductance is activated by depolarizing voltage steps to test potentials of -40 mV or more. Under these conditions, the instantaneous current observed as soon as the depolarizing pulse is applied displays outward rectification and reverses near EC1. During the pulses, a strong inactivation is observed for potentials greater than + 40 mV. This conductance is independent of external and internal calcium.7. It is concluded that the gonadotrophins act through a cyclic AMP-dependent * To whom reprint requests should be addressed. N1I 8151 P. D CHA TELLE AND M. JOFFRE process to activate a Cl-conductance. This conductance is different to the hyperpolarization-activated Cl-conductance and the calcium-activated Clconductance also present in the membrane of resting cells.

Functional Assessment of the Calcium Messenger System in Cultured Mouse Leydig Tumor Cells: Regulation of Human Chorionic Gonadotropin-Induced Expression of the Steroidogenic Acute Regulatory Protein

“…K ϩ has been regarded as a Ca 2ϩ -mobilizing agent in adrenal cells through opening of T-and L-type transmembrane Ca 2ϩ channels that are progressively involved in steroid hormone biosynthesis (25,27). Our findings in mLTC-1 cells demonstrate that K ϩ markedly increased the levels of hCG-stimulated StAR mRNA and protein, in close coordination with acute P production.…”

“…The physiological action of K ϩ , especially in adrenal cells, is thought to involve the opening of plasma membrane Ca 2ϩ channels, facilitating the influx of Ca 2ϩ for activation of steroid hormone biosynthesis (25). In adrenal glomerulosa cells, ample evidence exists for the requirement of Ca 2ϩ for the steroidogenic action of K ϩ (26 -28).…”

Volume-activated chloride channels in mice Leydig cells

“…Biochemical evidences suggest that Cl − channels are involved in the steroidogenic process, as micromolar concentrations of DIDS and SITS decreased testosterone secretion, but the type of Cl − channels involved and the mechanisms are not yet completely understood [6,7,34,39]. Short pulses of human chorionic gonadotropin (hCG) or LH applied to these cells under isosmotic conditions lead to the activation of a transient outwardly rectifying Cl − conductance [14] similar to the Cl − background (Cl bg ) conductance observed in squid axons [20]. In addition, there are suggestions [31,32] that these Cl − currents are activated by hyperpolarization, deactivated by depolarization, and are also modulated by c AMP and cell swelling, indicating that rat Leydig cells express Cl − channels named Cl bg,cAMP,swelll .…”

Modulation of K+ conductances by Ca2+ and human chorionic gonadotrophin in Leydig cells from mature rat testis.

“…Effects of hCG on the outwardly rectifying potassium conductances in rat Leydig cells The effects of hCG on the ionic conductances have been previously investigated in Leydig cells which were bathed in a chloride-rich external solution and which were dialysed with a low-calcium solution lacking ATP and containing either 0 5 or 10 mm EGTA (Duchatelle & Joffre, 1990). In these experiments, hCG appeared mainly to increase a cyclic AMP-dependent chloride conductance.…”

“…Confrontation of these numbers with the Ca2+ sensitivity observed with internal Ca2+ buffers would indicate that this conductance may be largely inhibited at rest. This, and the fact that the hyperpolarization-activated chloride conductance is not activated at rest, would explain the low resting membrane potential of the cells, measured either with the intracellular microelectrode technique (Joffre et al 1984a) or with the 'zero current' mode of the patch-clamp technique (Duchatelle & Joffre, 1990); this would also explain the weak dependence of the resting membrane potential on external potassium (Joffre, Mlollard, Regondaud & Gargouil, 1984b). However, the possibility should be kept in mind that, as in human T-lymphocytes (Schlichter et al 1993), the calciumdependent inhibition of the resting potassium conductance could be modulated by the cytosol.…”