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

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Abstract
Conventional microelectrode techniques were used to study the passive electrical properties of salivary glands from C. nuditarsis insect larvae of the 4th 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 .mu.F [microfarad] cm-2. The multicellular glands were reduced to intact 2-cell preparations by destroying neighboring cells mechanically. Each cell of a coupled cell pair was impaled with 2 microelectrodes, one to pass rectangular current pulses and the other to monitor the resulting voltage deflexions. Internal consistency tests revealed that the observed conditions may be described accurately by an equivalent circuit consisting of a delta configuration of 3 resistive elements: the resistances of the nonjunctional membrane of cell 1 and cell 2 (r1 and r2) and the resistance of the gap junctional membrane connecting the 2 cells (rg). The current-voltage relation of the nonjunctional 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 (.apprx. .+-. 10 mV). Individual values of rg varied from 20-3800 k.OMEGA., with an overall mean of 1100 k.OMEGA.. The lower values are thought to represent the physiological state of cellular coupling; 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.