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Department of Biomedical Sciences, Cornell University, Ithaca, New York 14853
The role of Ca2+ in mediating
the diuretic effects of leucokinin-VIII was studied in isolated
perfused Malpighian tubules of the yellow fever mosquito, Aedes
aegypti. Peritubular leucokinin-VIII (1 µM) decreased the
transepithelial resistance from 11.2 to 2.6 k
· cm, lowered
the transepithelial voltage from 42.8 to 2.7 mV, and increased
transepithelial Cl
diffusion potentials 5.1-fold. In
principal cells of the tubules, leucokinin-VIII decreased the
fractional resistance of the basolateral membrane from 0.733 to 0.518. These effects were reversed by the peritubular Ca2+-channel
blocker nifedipine, suggesting a role of peritubular Ca2+
and basolateral Ca2+ channels in signal transduction. In
Ca2+-free Ringer bath, the effects of leucokinin-VIII were
partial and transient but were fully restored after the bath
Ca2+ concentration was restored. Increasing intracellular
Ca2+ with thapsigargin duplicated the effects of
leucokinin-VIII, provided that peritubular Ca2+ was
present. The kinetics of the effects of leucokinin-VIII is faster than
that of thapsigargin, suggesting the activation of inositol-1,4,5-trisphosphate-receptor channels of intracellular stores.
Store depletion may then bring about Ca2+ entry into
principal cells via nifedipine-sensitive Ca2+ channels in
the basolateral membrane.
nifedipine; thapsigargin
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