Effects of leucokinin-VIII on Aedes Malpighian tubule segments lacking stellate cells.

Abstract

The diuretic peptide leucokinin is known to increase fluid secretion in Malpighian tubules of the yellow fever mosquito Aedes aegypti by increasing a transepithelial Cl(-) conductance. The present study sought to examine whether stellate cells provided this transepithelial conductance in Aedes Malpighian tubules as they do in Drosophila Malpighian tubules. Aedes Malpighian tubule segments with and without stellate cells were perfused in vitro for measurements of the transepithelial voltage (V(t)), resistance (R(t)) and Cl(-) diffusion potentials (DP(Cl)). In 11 tubule segments containing both principal cells and stellate cells, 1 micro mol l(-1) leucokinin-VIII added to the peritubular bath immediately and significantly decreased V(t) from 39.3+/-14.3 mV to 2.3+/-0.7 mV, decreased R(t) from 12.4+/-2.6 kOmegacm to 2.4+/-0.3 kOmegacm, and increased DP(Cl) from 8.2+/-1.2 mV to 42.1+/-5.4 mV. These effects of leucokinin-VIII were qualitatively and quantitatively similar in six tubule segments containing no stellate cells; V(t) decreased from 37.8+/-7.0 mV to 3.4+/-0.6 mV, R(t) decreased from 8.8+/-2.1 kOmegacm to 1.7+/-0.2 kOmegacm, and DP(Cl) increased from 5.8+/-2.6 mV to 50.0+/-2.1 mV. Thus, stellate cells are not required for signaling or mediating the effects of leucokinin in Malpighian tubules of Aedes aegypti. The results further support previous observations that principal cells signal the effects of leucokinin to increase the Cl(-) conductance of the paracellular pathway through septate (or tight) junctions.