title: Spontaneous and GABA-evoked chloride channels on pituitary intermediate lobe cells and their internal Ca requirements.
abstract: On porcine intermediate lobe (IL) endocrine cells, spontaneously opening chloride channels have been studied and compared to GABA-A activated chloride channels. Elementary currents were recorded mainly from outside-out patches excised from IL cells maintained in culture for 1-4 weeks. Spontaneous inward currents were observed in Cs-loaded cells after replacing Na in the extracellular medium by the impermeant ion choline. This activity, at an internal calcium concentration of 10(-8) M corresponded to a channel for chloride ions with a main conductance level of 26 pS, and substates around 11 pS. The sequence of permeabilities to halides was I greater than Br greater than Cl. These conductance characteristics were common to the GABA-operated channels which also showed a main conductance substate of 23-31 pS. The open time of the 26 pS level mostly encountered in spontaneous activity, was distributed along two modes: one, the most frequent, around 1 ms, and the other around 4 ms. This latter mode was the predominant one observed during GABA and isoguvacine applications but in addition a bursting activity of 19 ms duration was also seen. Specific GABA-A receptor antagonists (bicuculline and SR42641, 1 microM) blocked activity evoked by GABA (1-10 microM), but did not affect spontaneous events. These spontaneous Cl events were only observed in a restricted range of internal Ca concentrations, i.e. between 1 nM and 0.1 microM, and were practically abolished at Cai 1 microM. The GABA-induced activity of Cl channels was also Ca-sensitive, being reduced when Cai reached 1 microM.
mesh_terms: D000818:Animals; D002118:Calcium / Q000502:physiology; D002478:Cells, Cultured; D002712:Chlorides / Q000378:metabolism; D007473:Ion Channels / Q000187:drug effects / Q000502:physiology*; D007477:Ions / Q000378:metabolism; D007539:Isonicotinic Acids / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects; D010902:Pituitary Gland / Q000187:drug effects / Q000378:metabolism*; D011963:Receptors, GABA-A / Q000187:drug effects / Q000502:physiology; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology*
chemical_list: D002712:Chlorides; D007473:Ion Channels; D007477:Ions; D007539:Isonicotinic Acids; D011963:Receptors, GABA-A; D005680:gamma-Aminobutyric Acid; D002118:Calcium; C015300:isoguvacine