Cytosolic chloride ions stimulate Ca(2+)-induced exocytosis in melanotrophs.

We used the whole-cell patch-clamp technique to study the secretory activity of single cells by monitoring changes in membrane capacitance [Neher, E. and Marty, A. (1982) Proc. Natl. Acad. Sci. USA 79, 523-535] in anterior pituitary cells. Unexpectedly we have observed that increasing intracellular chloride ions stimulate Ca(2+)-induced exocytosis in a dose-dependent fashion (Kd = 12 mM). These results demonstrate a role of cytosolic chloride ions in the regulation of exocytotic secretion in anterior pituitary cells. It is suggest that chloride channels, in addition to playing a part in regulating membrane electrical activity [Korn, S.J., Bolden, A. and Horn, A. (1991) J. Physiol. 439, 423-437; Penner, R., Matthews, G. and Horn, A. (1988) Nature 334, 499-504] and cytosolic pH [Kaila, K. and Voipio, J. (1987) Nature 330, 163-165], are also involved in the modulation of cytosolic chloride concentration and thus in the control of exocytosis.