Modulation of voltage-dependent Ca2+ conductance by changing Cl- concentration in rat lactotrophs.
In pituitary cells, voltage-dependent Ca2+ channels play an important role in such physiological processes as exocytosis, secretion, the cell cycle, and proliferation. Thus mechanisms that modulate voltage-dependent Ca2+ channel activity participate indirectly in regulating intracellular Ca2+ concentration. We have shown a new modulating mechanism for voltage-dependent Ca2+ channels by demonstrating that Ca2+ influx is influenced by Cl-. To evaluate the role of Cl- on Ca2+ conductance coupling, we first measured the intracellular Cl- concentration of rat lactotrophs using the Cl(-)-sensitive fluorescence probe sulfopropylquinolinium by simple microspectrofluorometry or combined with electrophysiology. We found an average intracellular Cl- concentration of rat lactotrophs of approximately 60 mM (n = 39). Using the whole cell tight-seal recording technique, we showed that a reduction in external Cl- concentration ([Cl-]o) and a decrease in Cl- conductances affected Ca2+ conductance as measured by Ba2+ movement through the Ca2+ channels (I(Ba)). Low [Cl-]o (39 mM) induced a decrease in Ca2+ entry via voltage-gated Ca2+ channels (-27.75 +/- 4% of normalized I(Ba)). Similarly, blockade of the Cl- conductance by 1 mM 9-anthracene carboxylic acid induced a decrease in I(Ba) (-26 +/- 6% of normalized I(Ba)). This modulation of I(Ba) was inhibited by 24-h pretreatment of the cells with pertussis toxin (1 microg/ml), suggesting that changes in Cl- concentration induced by low [Cl-]o and 9-anthracene carboxylic acid interfered with the phosphorylation of G proteins involved in Ca2+ channel activation. These results suggest a feedback mechanism based on constant interaction between Ca2+ and Cl-. Finally, they also emphasize the physiological role of Cl- in rat lactotrophs.
Garcia
L
L
Centre National de la Recherche Scientifique Unité Mixte de Recherche,Universite de Bordeaux II, France.
Fahmi
M
M
Prevarskaya
N
N
Dufy
B
B
Sartor
P
P
D000818:Animals; D000873:Anthracenes / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism / Q000502:physiology*; D018118:Chloride Channels / Q000037:antagonists & inhibitors; D002712:Chlorides / Q000378:metabolism*; D006224:Cricetinae; D004553:Electric Conductivity; D004594:Electrophysiology; D005260:Female; D007425:Intracellular Membranes / Q000378:metabolism; D009994:Osmolar Concentration; D010903:Pituitary Gland, Anterior / Q000166:cytology / Q000378:metabolism / Q000502:physiology*; D011388:Prolactin / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar
D000873:Anthracenes; D018118:Chloride Channels; D002712:Chlorides; C010030:9-anthroic acid; D011388:Prolactin; D002118:Calcium