Fig. 11. Estimates of electrophysiological variables in the Malpighian tubule of the yellow fever mosquito. All values are normalized to cm tubule length. (A) The tubule modeled as a single cable (data from Pannabecker et al., 1992). The radial resistance is the transepithelial resistance consisting of the resistances of the apical membrane R_a, basolateral membrane R_bl and the shunt R_sh. The axial resistance of the tubule is the core resistance R_co. (B) The tubule modeled as a double cable. Here the axial resistance consists of the lumen resistance R_lu and the gap-junction resistance R_gap. In both models the transepithelial voltage V_t and the basolateral (V_bl) and apical (V_a) membrane voltages are the same. E, electromotive force; D_e is the electrical diameter of the tubule lumen calculated from the lumen resistance R_lu (Pannabecker et al., 1992).