Abstract
When isolated snail ganglia were incubated at 25° in a medium containing 14C-histamine, tissue:medium ratios of about 4 were obtained after only 5 min. Metabolism of the accumulated amine is rapid, for even within this short incubation period, 20 per cent of the substance was metabolised. The process responsible for this accumulation showed properties of an active transport system: it was temperature-sensitive, sodium dependent, and particularly inhibited by ouabain, phenoxybenzamine, chlorpromazine and desimipramine. The accumulation of 14C-histamine showed saturation kinetics typical of a carrier-mediated process and can be divided into sodium-sensitive and -insensitive components. Kinetic analysis of the data revealed similar K m values for both sodium-sensitive and sodium-insensitive plus -sensitive components, i.e. 10 −5 M. A rapid efflux of radioactivity from tissue loaded with 14C-histamine was observed when exposed to 70 mM KCl. This release was inhibited when the calcium content in the medium was replaced by sucrose. Moreover, cobalt ions added to the incubation medium counteracted the effect of KCl. The discussion of the present results is based on the hypothesis that histamine has a transmitter function in the snail CNS.
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