Fig. 4. Measurement of the gap-junction resistance between principal cells of isolated Malpighian tubules of the yellow fever mosquito Aedes aegypti. (A) The measuring circuit in the tubule modeled as a double cable; (B) reduction of the circuit by eliminating R_sh via the short-circuiting effects of leucokinin-VIII; (C) further reduction of the circuit by combining the parallel resistances in circuit in B. The electromotive forces (E) are neglected in C as they should not be affected by voltage-clamping cell 1. V, R and I have their usual meaning; a, apical membrane; bl, basolateral membrane; lu, tubule lumen; gj, gap junction; nj, non-junction. The non-junctional resistance R_nj includes R_a, R_bl and R_lu.