Abstract
The low Ca2+ + tetraethylammonium (TEA) medium enhanced electrically evoked norepinephrine release by 3.5-fold in canine saphenous veins. ω-Conotoxin GVIA (ω-CTX) inhibited the neurotransmission more markedly in low Ca2+ + TEA medium than in normal Krebs medium. This is the case for the inhibition by tetrodotoxin, though to a lesser extent. The inhibition by ω-CTX was competitively antagonized by elevating external Ca2+ The results indicate that low Ca2+ + TEA medium is useful for studying the effect of Ca antagonists on adrenergic neurotransmission, because ω-CTX acts more effectively in this medium.
