Transepithelial voltage measurements in isolated Malpighian tubules of Aedes aegypti

• Published in: Journal of insect physiology Vol. 35; no. 1; pp. 41 - 52
• Main Authors: Aneshansley, D.J., Marler, C.E., Beyenbach, K.W.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 1989
• Subjects: Aedes aegypti; circuit analysis; circuits; Culicidae; electric potential; electrophysiology; isolated perfused tubules; Malpighian tubules; mathematical models; mosquito; physiology; Ramsay method; short-circuits; Transepithelial voltage; Transepithelial voltage; isolated perfused tubules; short-circuits; circuit analysis; Ramsay method; Malpighian tubules; mosquito
• ISSN: 0022-1910; 1879-1611
• DOI: 10.1016/0022-1910(89)90034-6

Three methods to measure the transepithelial voltage were evaluated in isolated Malpighian tubules of the yellow fever mosquito, Aedes aegypti. In method I the lumen-to-bath voltage ( V T.p) was measured in isolated perfused tubules through a perfusion pipette lodged in the tubule lumen. Measured voltages were exclusively lumen-positive, 46.0 ± 1.7 mV, X ± SEM , n = 185. In method II the voltage ( V out ) was measured in secreting tubules as the voltage between the secreted fluid droplet and the Ringer bath. This voltage measurement yielded positive and negative values, on average positive, 10.5 ± 2.8 mV, n = 108. Both measurements are supposedly indirect indicators of the transepithelial potential, based on the assumption that the measurements are of open circuit voltages, that is, there are no closed circuit paths over which the transepithelial voltage could be divided. In fact, there are such paths in the oil-bathed tubule segment of method II. Analysis of the measuring circuit in method II reveals (I) the peritubular water film to effect the amplitude of the measured voltage, and (2) the axial lumen resistance and the lateral resistance of the epithelial wall to affect the amplitude and the polarity of the measured voltages. This conclusion is supported by method III where voltage is measured in secreting tubules via a microelectrode impaling the tubule lumen. The microelectrode voltage measurements ( V T. m ) are always lumen-positive as in method I even though method II yields negative voltages ( V out ) at the same time.