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EFFECTS OF TETRODOTOXIN AND MONENSIN ON THE NORADRENALINE OUTPUT INDUCED BY OUABAIN FROM THE GUINEA‐PIG VAS DEFERENS IN THE PRESENCE OF VARIOUS DIVALENT CATIONS
Author(s) -
Nakazato Yoshikazu,
Ito Shigeo,
Ohga Akira
Publication year - 1989
Publication title -
quarterly journal of experimental physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.925
H-Index - 101
eISSN - 1469-445X
pISSN - 0144-8757
DOI - 10.1113/expphysiol.1989.sp003292
Subject(s) - ouabain , divalent , monensin , tetrodotoxin , chemistry , incubation , vas deferens , extracellular , medicine , endocrinology , sodium , biophysics , biochemistry , biology , organic chemistry
The importance of Na + in the ouabain‐induced increase in noradrenaline output from adrenergic nerve terminals of the guinea‐pig vas deferens was investigated during incubation in standard Krebs solution and Sr 2+ ‐ and Ba 2+ −substituted Krebs solutions. Ouabain (10 −4 M) caused a gradual increase in noradrenaline output regardless of the type of divalent cation used. The rate of development of the ouabain‐induced noradrenaline output and the maximum amount released depended on the divalent cation present (Ba 2+ 〉 Sr 2+ 〉 Ca 2+ ). The magnitude of the ouabain‐induced response depended on the concentration of extracellular Na + . The sensitivity of the ouabain‐induced response to a change in Na + concentration depended on the divalent cation present (Ca 2+ 〉 Sr 2+ 〉 Ba 2+ ). Tetrodotoxin (1·6 x 10 −6 M) delayed the onset, whereas monensin (10 −5 M) hastened it. The maximum level of the ouabain‐induced response was attenuated by monensin in all the incubation solutions. These results suggest that Na + entry into adrenergic nerve terminals through tetrodotoxin‐sensitive mechanisms is crucial for the increase in noradrenaline output due to ouabain when extracellular Ca 2 + is replaced with Sr 2+ or Ba 2+ .