Electrical coupling between cells of the insect Aedes albopictus.

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Abstract
1. Cell pairs of an insect cell line (Aedes albopictus, clone C6/36) were used to study the electrical properties of intercellular junctions. A double voltage-clamp approach was adopted to control the voltage gradient between the cells and measure the intracellular current flow. 2. Determinations of junctional conductance (g(j)) revealed two types of intercellular contacts, gap junctions and cytoplasmic bridges. Identification occurred by means of functional criteria, i.e. the dependency of g(j) on (i) junctional membrane potential, (ii) non-junctional membrane potential, and (iii) heptanol. 3. In cells pairs with putative gap junctions, g(j) was dependent on the junctional membrane potential (V(j)). When determined at the beginning of voltage pulses, g(j) was insensitive to V(j); when determined at the end of 15 s pulses, it depended on V(j) in a bell-shaped manner (70% decrease for a change in V(j) of +/- 75 mV). 4. These cell pairs also showed a dependency of g(j) on the non-junctional membrane potential (V(m)). When determined immediately after changing the non-junctional membrane potential in both cells, g(j) was not affected by V(m); when determined 30 s later, g(j) was modified by V(m) in a S-shaped fashion (100% decrease when V(m) was depolarized to +50 mV). 5. Exposure to 3 mM-heptanol gave rise to complete and reversible block of g(j) in cell pairs with putative gap junctions. 6. Cell pairs susceptible to uncoupling by heptanol revealed junctional currents indicative of the operation of gap junction channels. The single-channel conductance, determined at a V(m) of -50 to -70 mV, was 133 pS. 7. In the case of putative cytoplasmic bridges, g(j) was insensitive to the junctional and non-junctional membrane potential. In addition, it was not affected by 3 mM-heptanol. 8. While most cell pairs showed functional properties characteristic of gap junctions or cytoplasmic bridges, few cell pairs exhibited junctional currents compatible with the co-existence of both junctional structures.