Activation of neurohypophysial vasopressin release by Ca2+ influx and intracellular Ca2+ accumulation in the rat.
1. Isolated rat neurohypophyses were stimulated electrically in an in vitro perifusion system. A Ca2(+)-sensitive microelectrode was placed in the centre of each neurohypophysis and [Ca2+]o decrease evoked by the stimulation were determined. 2. In neurohypophyses injected with Fura-2 AM (acetoxymethyl ester), increases and decreases in fluorescence excited at 340 and 380 nm, respectively, were evoked by stimulation. The time course of the fluorescence changes was similar to that of [Ca2+]o decreases, suggesting that the [Ca2+]o changes mirrored [Ca2+]i increases. 3. Calcium influx into neurosecretory axons and terminals was estimated as the difference in [Ca2+]o decrease rates immediately before and after train pulse stimulation. 4. Vasopressin release from the neurohypophysis, measured by specific radioimmunoassay, was facilitated by stimulation in parallel with a parameter of [Ca2+]o decrease multiplied by Ca2+ influx. 5. The O2 consumption rate, estimated as rate of PO2 decrease in the tissue, was facilitated by stimulation in parallel with [Ca2+]o decreases. 6. Possible calcium-dependent mechanisms of vasopressin release, and the energy-dependent step of the release by Ca2+, are discussed.
Shibuki
K
K
Department of Physiology, Jichi Medical School, Tochigi-ken, Japan.
D000818:Animals; D001369:Axons / Q000502:physiology; D001572:Benzofurans; D002118:Calcium / Q000502:physiology*; D016257:Fura-2; D066298:In Vitro Techniques; D008297:Male; D009411:Nerve Endings / Q000502:physiology; D009489:Neurosecretion / Q000502:physiology; D010101:Oxygen Consumption / Q000502:physiology; D010904:Pituitary Gland, Posterior / Q000502:physiology*; D051381:Rats; D011919:Rats, Inbred Strains; D013997:Time Factors; D014667:Vasopressins / Q000378:metabolism*
D001572:Benzofurans; D014667:Vasopressins; D002118:Calcium; D016257:Fura-2