Some factors affecting the extraneuronal accumulation of adrenaline in guinea-pig trachealis smooth muscle cells

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Abstract
Tracheal segments from guinea-pigs pretreated with 6-hydroxydopamine were incubated in 5 or 200 μmol·l−1 adrenaline at 37°C. Catechol-O-methyltransferase and monoamine oxidase were inhibited by U-0521 and pargyline, respectively, and the accumulation of adrenaline in trachealis smooth muscle cells was measured by fluorescence microphotometry. The effects of anoxia, anoxia plus glucose deprivation, ouabain, reduced sodium (Na+) concentration, elevated potassium (K+) concentration and calcium (Ca2+) deprivation on adrenaline accumulation were examined in tissues incubated in adrenaline for 5 min. Adrenaline accumulation in the trachealis smooth muscle cells was reduced by inhibition of oxidative metabolism (anoxia and glucose deprivation), by ouabain (100 μmol·l−1), by a reduction in Na+ concentration from 139 mmol·l−1 to 25 mmol·l−1, and by increases in K+ concentration, but not by omission of Ca2+. These results from guinea-pig trachealis smooth muscle cells, in combination with those obtained by other workers on various organs and tissues, indicate that the extraneuronal accumulation of catecholamines requires energy derived from oxidative metabolism and is very sensitive to inhibition by increases in K+ concentration. However, there is marked variability in the effects of ouabain and of reduced Na+ or Ca2+ concentrations on the accumulation.

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