Potassium and chloride conductances in rat Leydig cells: effects of gonadotrophins and cyclic adenosine monophosphate.
1. 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 microM) 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 ECl. 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 process to activate a Cl- conductance. This conductance is different to the hyperpolarization-activated Cl- conductance and the calcium-activated Cl-conductance also present in the membrane of resting cells.
Duchatelle
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P
Laboratoire de Physiologie Animale, CNRS:URA 290, Faculté des Sciences, Université de Poitiers, France.
Joffre
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M
D000818:Animals; D018118:Chloride Channels; D006063:Chorionic Gonadotropin / Q000494:pharmacology*; D000242:Cyclic AMP / Q000502:physiology*; D004553:Electric Conductivity; D006160:Guanosine Triphosphate / Q000502:physiology; D007473:Ion Channels / Q000187:drug effects; D007985:Leydig Cells / Q000187:drug effects / Q000502:physiology*; D007986:Luteinizing Hormone / Q000494:pharmacology*; D008297:Male; D008565:Membrane Proteins / Q000187:drug effects*; D015221:Potassium Channels / Q000187:drug effects*; D051381:Rats; D011919:Rats, Inbred Strains
D018118:Chloride Channels; D006063:Chorionic Gonadotropin; D007473:Ion Channels; D008565:Membrane Proteins; D015221:Potassium Channels; D006160:Guanosine Triphosphate; D007986:Luteinizing Hormone; D000242:Cyclic AMP