AJP - Regulatory, Integrative and Comparative Physiology, Vol 244, Issue 5 703-R708, Copyright © 1983 by American Physiological Society
Role of calcium in osmotic and nonosmotic release of vasopressin from rat organ culture
S. Ishikawa and R. W. Schrier
In the present study the role of calcium (Ca) in the stimulation of
arginine vasopressin (AVP) release from the cultured rat
hypothalamoneurohypophyseal complex (HNC) was examined in response to three
different stimuli, 56 mM potassium chloride, an increase in medium
osmolality from 290 to 310 mosmol/kg H2O, or 1 X 10(-6) M angiotensin II
(ANG II). With all three stimuli AVP release from rat HNC explants was
enhanced by increasing Ca concentration in the medium from 0 to 1.8 mM Ca.
However, high concentrations of Ca (8 mM) inhibited the response of AVP
release to either hyperosmolality or angiotensin II. Chemically dissimilar
blockers of cellular Ca uptake, verapamil (5.2 X 10(-6) or 5.2 X 10(-5) M)
or nifedipine (5.8 X 10(-6) or 5.8 X 10(-5) M), completely abolished AVP
release from rat HNC explants in response to the three different stimuli in
1.8 mM Ca. In a normal concentration of medium Ca (1.8 mM) a Ca ionophore,
A23187 (3.8 X 10(-5) M), significantly enhanced the osmotic and nonosmotic
(ANG II-stimulated) release of AVP from rat HNC explants compared with
controls without Ca ionophore. This effect of Ca ionophore to enhance AVP
release was more evident in a lower Ca medium (0.9 mM Ca in the
hyperosmolality study and 0.3 mM Ca in the ANG II study). These results
therefore indicate that cellular Ca uptake is an important modulator of
osmotic and nonosmotic AVP release from the intact rat
hypothalamoneurohypophyseal system. The influence of extracellular Ca on
the osmotic and nonosmotic release of AVP is also demonstrated.
