Electric current flow in a two-cell preparation from Chironomus salivary glands

Conventional micro-electrode techniques were used to study the passive electrical properties of salivary glands from Chironomus nuditarsis insect larvae of the fourth instar stage. Linear cable analysis performed on intact glands revealed the following constants: axial intracellular resistance, Ri = 2730 omega cm; membrane resistance per unit apparent cylindrical area, Rm = 1350 omega cm2; membrane capacitance per unit apparent cylindrical area, Cm = 17.6 microF cm-2. The multicellular glands were reduced to intact two-cell preparations by destroying neighbouring cells mechanically. Each cell of a coupled cell pair was impaled with two micro-electrodes, one to pass rectangular current pulses and the other to monitor the resulting voltage deflexions. Internal consistency tests revealed that the experimental data under steady-state conditions may be described accurately by an equivalent circuit consisting of a delta configuration of three resistive elements: the resistances of the non-junctional membrane of cell 1 and cell 2 (r1 and r2), and the resistance of the gap junctional membrane connecting the two cells (rg). The current-voltage relation of the non-junctional membrane was found ohmic over a membrane potential ranging from -40 mV to + 10 mV. The mean value of Rm was 2020 omega cm2. The resistance function of the gap junctional membrane was also ohmic. There was no dependence of gap junctional resistance on voltage or direction of current flow, at least over the relatively narrow range of potentials tested (approximately +/- 10 mV). Individual values of rg varied from 20 to 3800 k omega, with an over-all mean of 1100 k omega. The lower values are thought to represent the physiological state of cellular coupling, whereas the higher ones may reflect partial uncoupling caused by local damage. The proposed cell pair is a suitable preparation for studying problems related to intercellular coupling.