Oscillations of voltage and resistance in Malpighian tubules of Aedes aegypti

The transepithelial voltage (V-t) of isolated Malpighian tubules of the yel low fever mosquito Aedes aegypti spontaneously oscillates in more than half the tubules. Typically, V-t decreases and then rises at a frequency of 2 o scillations/min with a duration of 16 s. In 6 isolated perfused tubules stu died in detail, V-t oscillates between 50.5 mV and 15.7 mV in parallel with (1) oscillations of the transepithelial resistance (R-t) between 7.61 k Oh m cm and 3.63 k Ohm cm, (2) oscillations of the basolateral membrane voltag e 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 R -t decreases during the oscillations V-t goes to the transepithelial equili brium potential of Cl (E-cl) indicating transient changes in transepithelia l Cl conductance as the mechanism of voltage and resistance oscillations. S ince the largest voltage oscillations take place across the whale epitheliu m and not across cell membranes, oscillating Cl conductances are localized to a single transepithelial Cl diffusion barrier such as the paracellular p athway. This conclusion is supported by the analysis of electrically equiva lent circuits that identify the shunt pathway as the site of oscillating Cl conductances. (C) 2000 Elsevier Science Ltd. All rights reserved.