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The FASEB Journal, Vol 2, 2907-2912, Copyright © 1988 by The Federation of American Societies for Experimental Biology

RESEARCH COMMUNICATIONS

Vasopressin enhances a calcium current in human ACTH-secreting pituitary adenoma cells

P Mollard, P Vacher, MA Rogawski and B Dufy
Laboratory of Neurophysiology, National Center for Scientific Research, Bordeaux, France.

Arginine vasopressin (AVP) is a potent secretagogue for adrenocorticotropin (ACTH) release from normal corticotropes and from ACTH-secreting pituitary adenoma cells. To explore the mechanism underlying this action, we investigated the effects of AVP on Ca2+- dependent action potentials and Ca2+ currents in cultured human ACTH- containing pituitary tumor cells (hACTH adenoma cells). Pituitary adenoma fragments removed at surgery from two patients with Cushing's disease were dispersed, and the isolated cells were grown in monolayer culture. Most of the cells showed ACTH immunoreactivity that persisted even after as much as 2 months in culture. Current clamp and voltage clamp recordings were carried out using the patch-clamp technique in the whole cell configuration. AVP produced an increase in the amplitude and duration of action potentials in these cells, and substantially enhanced the transient after-hyperpolarization after each spike. Under voltage the transient after-hyperpolarization after each spike. Under voltage clamp, hACTH adenoma cells showed two Ca2+ current components: a low-threshold, rapidly inactivating (T-type) current; and a higher threshold, slowly inactivating (L-type) current. AVP markedly increased the amplitude of the L-type current without affecting the T-type current. These data suggest that AVP may enhance Ca2+ entry associated with action potentials by potentiating the activity of L-type Ca2+ channels. The resulting rise in cytosolic free Ca2+ may be a key link in the process by which AVP stimulates ACTH release in the pituitary.


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A. Tse and A. K. Lee
Arginine Vasopressin Triggers Intracellular Calcium Release, a Calcium-Activated Potassium Current and Exocytosis in Identified Rat Corticotropes
Endocrinology, May 1, 1998; 139(5): 2246 - 2252.
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Copyright © 1988 by The Federation of American Societies for Experimental Biology.