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Barium and strontium can substitute for calcium in noradrenaline output induced by excess potassium in the guinea‐pig.
Author(s) -
Nakazato Y,
Onoda Y
Publication year - 1980
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.1980.sp013349
Subject(s) - strontium , chemistry , divalent , barium , calcium , potassium , vas deferens , guinea pig , medicine , endocrinology , inorganic chemistry , biology , organic chemistry
1. The ability of Ba2+ and Sr2+ to substitute for Ca2+ in the noradrenaline output induced by excess K+ was examined using isolated guinea‐pig vas deferens. 2. When the vas deferens was repeatedly exposed to excess K+ (60 mM) at 40 min intervals, the noradrenaline output increased at least three‐fold in incubation medium which contained either Ca2+, Ba2+ or Sr2+. The response decreased on repetition. The order of effectiveness was roughly Ba2+ > Ca2+ > Sr2+. 3. In the absence of excess K+, these cations had no significant stimulating effect on the noradrenaline output even when added after exposure to Ca2+‐free solution. 4. As the concentration of divalent cation was increased from 0.2 to 2.5 mM the noradrenaline output induced by excess K+ increased. The maximum noradrenaline output was achieved at a divalent cation concentration of 2.5 mM and was 29.56 +/‐ 3.52, 15.02 +/‐ 1.12 and 7.45 +/‐ 0.84 (mean +/‐ S.E. of mean) n‐mole/g per hr in the presence of either Ba2+, Ca2+ or Sr2+, respectively. Further increase in the concentration of the cations reduced the response. 5. The addition of either Sr2+ (2 mM) or Ca2+ (1 mM) to a solution containing various concentrations of Ba2+ facilitated the K+‐induced increase in the noradrenaline output when the Ba2+ concentration was low, but inhibited release of noradrenaline when higher concentrations of Ba2+ were used. The addition of Sr2+ (1 mM) to Ca2+‐containing solutions had a similar effect. 6. Mg2+ competitively inhibited the K+‐induced increase in the noradrenaline output in the presence of either Ba2+ or Sr2+ and blocked that in the presence of CA2+. 7. The results indicate that both Ba2+ and Sr2+ can substitute for Ca2+ in the cations act though the same site at some stage in the process of K+‐induced transmitter release.