Modulation of voltage-dependent ca 2& conductance by changing
chloride ion concentration in rat lactotrophs.
Garcia, L., M Fahmi, N. Prevarskaya, B. Dufy, and P. Sartor.
LABORATOIRE DE NEUROPHYSIOLOGIE, CNRS UMR 5543, UNIVERSITE DE
BORDEAUX II, 146, rue L[acute]eo Saignat 33076 Bordeaux, FRANCE,
T[acute]el. (33) 5 57 57 15 51, Fax (33) 5 56 90 14 21
APStracts 3:0379C, 1996.
In pituitary cells, voltage-dependent Ca 2& channels are known to
play an important role in such physiological processes as exocytosis,
secretion, cell cycle and proliferation. Thus, mechanisms which
modulate voltage-dependent calcium channel activity participate
indirectly in regulating ([Ca 2& ]i). In this work we have shown
a new modulating mechanism for voltage-dependent Ca 2& channels,
by demonstrating that Ca influx is influenced by chloride. In order
to evaluate the role of chloride ions (Cl - ), on Ca 2&
conductance coupling, we started by measuring the [Cl - ]i of rat
lactotrophs, using the chloride-sensitive fluorescence probe sulfo
-propylquinolinium (SPQ), in simple microspectrofluorimetry or
combined with electrophysiology. We found the average [Cl - ]i of rat
lactotrophs to be about 60 mM, n = 39). Using the whole-cell, tight
-seal recording technique, we showed that both a reduction in external
Cl - concentration [Cl - ]o and a decrease in chloride conductances
affected calcium conductance as measured by Ba 2& ion movement
through the Ca 2& channels (IBa 2& ). Low [Cl - ]o (39 mM)
induced a decrease in calcium entry via voltage-gated calcium
channels (-27.75 &/- 4% of normalized I Ba 2&). Similarly,
blockade of the chloride conductance by 9-Anthracene Carboxylic-acid
(9AC, 1 mM) induced a decrease in I Ba 2& (-26 &/- 6% of
normalized I Ba 2&). This modulation of I Ba 2& was inhibited
by 24 hr pretreatment of the cells with pertussis toxin (PTX, 1
[mu]g/ml), suggesting that changes in chloride concentration induced
by low [Cl - ]o and 9AC interfered with the phosphorylation of G
proteins involved in calcium channel activation. These results
suggest a feedback mechanism based on constant interaction between Ca
2& and Cl - . Finally, they also emphasize the physiological role
of Cl - in rat lactotroph cells.
Received 5 December 1995; accepted in final form 11 November
1996.
APS Manuscript Number C729-5.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 31 December 1996