Abstract
The effects of 5-hydroxytryptamine, noradrenalin, adrenalin, octopamine and dopamine on the transepithelial voltage and fluid secretion of Malpighian tubules of Aedes aegypti were studied. Of these biogenic amines, only 5-hydroxytryptamine altered the transepithelial voltage. When applied in short pulses to superfused tubules, the transepithelial voltage depolarized rapidly and then hyperpolarized. The transepithelial resistance was reduced during both the depolarizing and hyperpolarizing phases of the response to 5-hydroxytryptamine. When added to the bathing saline at a concentration of 10 −6 M, the transepithelial voltage showed a more complex response with both depolarizing and hyperpolarizing elements. 5-Hydroxytryptamine was also the only biogenic amine tested that increased fluid secretion. The maximal increase of fluid secretion in response to 5-hydroxytryptamine was small compared to that of crude head extract, containing the putative diuretic hormones of this species. The concentration of potassium in secreted fluid of Malpighian tubules stimulated by 5-hydroxytryptamine was decreased by 20mM, while the sodium concentration showed an increase of similar magnitude.
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