The relationship between the membrane potential of neurosecretory nerve endings, as measured by a voltage-sensitive dye, and the release of neurohypophysial hormones.
The membrane potential of isolated rat neurohypophyses and isolated neurosecretosomes (neurosecretory nerve endings) was monitored with the voltage sensitive fluorescent probe diS-C3-(5). K ions, in contrast to Na or Cl ions, give rise to large changes of the fluorescent signal. The fluorescent response is linearly related to log[K+]0 at values higher than 10 mM, whereas at lower [K+]0 the permeability of the membrane for Na ions has to be taken into account. Veratridine increases the fluorescent signal only in the presence of external sodium; this effect is blocked by tetrodotoxin. After prolonged K-induced depolarisation, addition of veratridine to the medium gives a further change in fluorescence of diS-C3-(5) associated with release of vasopressin. Vasopressin release from isolated neurohypophyses started to increase significantly only above 25 mk [K+]0, while the depolarization of the membrane was linearly related to log[K+]0. The results are consistent with the view that neurosecretory nerve endings have voltage-dependent calcium channels that regulate the amount of hormone released during depolarisation.
D000818:Animals; D004573:Electrolytes / Q000378:metabolism; D007473:Ion Channels / Q000187:drug effects; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D009411:Nerve Endings / Q000187:drug effects / Q000502:physiology*; D009490:Neurosecretory Systems / Q000187:drug effects / Q000502:physiology*; D010904:Pituitary Gland, Posterior / Q000187:drug effects / Q000294:innervation*; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D013050:Spectrometry, Fluorescence / Q000379:methods; D013779:Tetrodotoxin / Q000494:pharmacology; D014667:Vasopressins / Q000378:metabolism*; D014701:Veratridine / Q000494:pharmacology
D004573:Electrolytes; D007473:Ion Channels; D014667:Vasopressins; D013779:Tetrodotoxin; D014701:Veratridine; D011188:Potassium