Calcium-activated chloride conductance of lactotrophs: comparison of activation in normal and tumoral cells during thyrotropin-releasing-hormone stimulation.
We studied a chloride (Cl-) conductance activated by calcium (Ca2+) in normal rat lactotrophs and compared its activation during TRH stimulation in normal rat lactotrophs and in GH3 tumoral lactosomatotrophs cells, using the whole-cell configuration of the patch-clamp technique. The Cl- specificity of the conductance was assessed by manipulation of internal and external Cl- concentrations. The reversal potentials were in agreement with those predicted by the Nernst equation. Ca2+ ionophore A23187 and membrane depolarizations activated the Cl- conductance. However, a feedback effect of Cl- gradient modifications on Ca2+ movements was also observed in normal lactotrophs. In the latter, TRH (100 nM) mobilization of intracellular Ca2+ activated this Cl- conductance together with the potassium (K+) conductance when both ions were present in the intracellular medium (IM) or alone when K+ was absent. Chloride conductance was not activated in the GH3 cells, where mobilization of intracellular Ca2+ by TRH (100 nM) activated only Ca2(+)-dependent K+ conductance. It seems likely that the activation of Cl- conductance in these two different cell types involves different mechanisms.
Sartor
P
P
Laboratoire de Neurophysiologie, URA CNRS 1200, Université de Bordeaux II, France.
Dufy-Barbe
L
L
Vacher
P
P
Dufy
B
B
D000818:Animals; D001692:Biological Transport / Q000187:drug effects / Q000502:physiology; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology*; D002463:Cell Membrane Permeability / Q000187:drug effects / Q000502:physiology; D002478:Cells, Cultured; D002712:Chlorides / Q000493:pharmacokinetics*; D005260:Female; D007150:Immunohistochemistry; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D010903:Pituitary Gland, Anterior / Q000166:cytology* / Q000502:physiology; D010911:Pituitary Neoplasms / Q000473:pathology* / Q000503:physiopathology; D011188:Potassium / Q000493:pharmacokinetics; D051381:Rats; D013050:Spectrometry, Fluorescence; D013973:Thyrotropin-Releasing Hormone / Q000494:pharmacology*; D014407:Tumor Cells, Cultured / Q000187:drug effects / Q000473:pathology
D002712:Chlorides; D000001:Calcimycin; D013973:Thyrotropin-Releasing Hormone; D011188:Potassium; D002118:Calcium