ISSN:
1573-6830
Keywords:
secretion
;
oxytocin
;
vasopressin
;
neurosecretosomes
;
ionomycin
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
Notes:
Summary 1. We studied the effects of extracellular sodium on the secretion of vasopressin (VP) and oxytocin (OT) and the efflux of45Ca from isolated, perfused nerve endings of the rat neurohypophysis (neurosecretosomes). 2. Upon removal of sodium from the perfusing medium, basal release of VP and OT increased by 3.95 ± 0.23- and 3.71 ± 0.22-fold, respectively, followed by a decline to about double the levels in normal (150 mM) sodium (P ⩽ 0.1). 3. Compared to neurosecretosomes perfused in normal (150 mM) sodium, omission of sodium from the medium augmented ionomycin-induced VP and OT secretion by 66 ± 5- and 20 ± 3-fold, respectively, and A23187-induced secretion was increased 1.3 ± 0.4- and 1.3 ± 0.1-fold (P ⩽ 0.01 for both ionophores). 4. The inhibition of ionomycin-induced secretion by sodium was concentration dependent (P ⩽ 0.01 for sodium ⩾ 5 mM); the IC50 was about 10 mM sodium for both hormones, and the Hill slope was close to -1. 5. The rate of45Ca efflux from neurosecretosomes showed 2.7 ± 0.1-fold stimulation upon increasing sodium from 4.5 to 150 mM (P ⩽ 0.01). 6. Our results suggest that sodium inhibits basal and stimulated secretion at the nerve terminal, possibly by reducing intraterminal calcium through sodium/calcium exchange.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00713276
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