Oscillations of voltage and resistance in Malpighian tubules of Aedes aegypti

The transepithelial voltage (Vt) of isolated Malpighian tubules of the yellow fever mosquito Aedes aegypti spontaneously oscillates in more than half the tubules. Typically, Vt decreases and then rises at a frequency of 2 oscillations/min with a duration of 16 s. In 6 isolated perfused tubules studied in detail, Vt oscillates between 50.5 mV and 15.7 mV in parallel with (1) oscillations of the transepithelial resistance (Rt) between 7.61 kΩcm and 3.63 kΩcm, (2) oscillations of the basolateral membrane voltage of principal cells between −56.7 mV and −72.2 mV, and (3) oscillations of the apical membrane voltage between 107.2 mV and 87.8 mV. The oscillations are dependent on the Cl concentration in the extracellular solutions. As Rt decreases during the oscillations Vt goes to the transepithelial equilibrium potential of Cl (Ecl) indicating transient changes in transepithelial Cl conductance as the mechanism of voltage and resistance oscillations. Since the largest voltage oscillations take place across the whole epithelium and not across cell membranes, oscillating Cl conductances are localized to a single transepithelial Cl diffusion barrier such as the paracellular pathway. This conclusion is supported by the analysis of electrically equivalent circuits that identify the shunt pathway as the site of oscillating Cl conductances.