Spontaneous and GABA-evoked chloride channels on pituitary intermediate lobe cells and their internal Ca requirements

Pflugers Arch. 1987 Aug;409(6):620-31. doi: 10.1007/BF00584663.

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Calcium / physiology
  • Cells, Cultured
  • Chlorides / metabolism
  • Ion Channels / drug effects
  • Ion Channels / physiology*
  • Ions / metabolism
  • Isonicotinic Acids / pharmacology
  • Membrane Potentials / drug effects
  • Pituitary Gland / drug effects
  • Pituitary Gland / metabolism*
  • Receptors, GABA-A / drug effects
  • Receptors, GABA-A / physiology
  • gamma-Aminobutyric Acid / pharmacology*

Substances

  • Chlorides
  • Ion Channels
  • Ions
  • Isonicotinic Acids
  • Receptors, GABA-A
  • gamma-Aminobutyric Acid
  • Calcium
  • isoguvacine