Temperature dependent sensitivity of isolated guinea-pig atria to sympathomimetic amines

Abstract

The role of neuronal uptake of sympathomimetic amines in the temperature-dependent supersensitivity to norepinephrine has been investigated at 37°C and at 26°C in isolated guinea-pig atria. Measurement of the uptake of 14C-dl-norepinephrine showed a significantly lower tissue-to-medium ratio at 26°C as compares to 37°C. Preincubation with 1 × 10 −5 M cocaine, a concentration which reduces the tissue-to-medium ratio to approximately 1 at both temperatures, does not prevent temperature-induced supersensitivity to the positive chronotropic effect of norepinephrine. Furthermore, at the lower bath temperature, supersensitivity to the positive chronotropic effect of isoproterenol was found under control conditions and also after preincubation with cocaine. The results are discussed in relation to the mechanism or mechanisms responsible for production of temperature-dependent supersensitivity.