The Effects of Small Molecule VU573 and Barium on Malpighian Tubule Electrophysiology of the Yellow Fever Mosquito Aedes aegypti

Abstract

VU573 is a synthetic organic molecule weighing 350 daltons, found to block inwardly-rectifying potassium (Kir) channels in high-throughput screening. In order to evaluate VU573 as a novel pesticide capable of inducing mosquito renal failure, electrophysiological analyses were carried out on isolated Malpighian tubules from the female yellow fever mosquito Aedes aegypti. Using the Malpighian tubule electrophysiology protocol developed in the laboratory of Klaus W. Beyenbach, exposure to 10µM peritubular VU573 was found to (1) hyperpolarize the basolateral membrane of isolated tubules by an average of 6.76 ± 1.27 mV (p<0.00012) and (2) increase cell input resistance by an average of 7.02 ± 1.31 kΩ (p<0.002) in conditions of potassium overload (34mM [K+] peritubular). These results confirm a block of A. aegypti Kir1 (AeKir1) expressed at the basolateral surface of stellate cells, which seem to be less involved in transport than their counterparts—the principal cells. Additional experiments establish that the 10µM VU573 dosage is equally as effective as the 50µM dosage (p=0.88). Furthermore, I-V plots taken of Malpighian tubules demonstrate that different tubules exhibit different degrees of rectification, from no rectification (Ohmic) to very strong rectification. The barium ion is known to strongly block all Kir channels. With the same protocol used for VU573, 5mM barium was tested and found to (1) hyperpolarize the tubule basolateral membrane by 11.91 ± 3.82 mV (p<0.008) and (2) increase cell input resistance by 123.58 ± 12.93 kΩ (p<0.0003). The much smaller resistance increase with VU573 compared to barium, coupled with the laboratory of Peter M. Piermarini’s finding of AeKir1 on stellate cells, suggests that AeKir1 channels are less involved with potassium transport and likely serve other functions, such as potassium sensing or cellular housekeeping. Taken in all, VU573 is effective at blocking AeKir1 but would need to be refined further to have an even more potent antidiuretic effect.