Voltage-dependent gap junctional conductance in hepatopancreatic cells of Procambarus clarkii

Properties of gap junction channels present between specific cell types constituting the hepatopancreas of the crayfish (Procambarus clarkii) were investigated using the dual whole cell voltage clamp technique. Four different cell types (E, Fe, R and B) were identified on the basis of their morphology using light and electron microscopy. Although junctional conductance (Gj) could not be measured in B-B cell pairs, junctional currents were resolved in both homologous and heterologous combinations of the other cell types. E-E, Fe-Fe, and E-Fe cell pairs exhibited strong dependence on inside-out voltage (Vi-o), such that Gj increased with hyperpolarization to a maximal plateau reached at approximately -40 mV and was abolished with depolarization > 10 mV. The Gj-Vi-o relationship can be described by a squared Boltzmann relation with A = 0.101 and V0 = 0.135 mV. In this system, sensitivity of the junctions to transjunctional voltage was slight, if present at all. Gating mechanisms were complex, as evidence by the presence of multiple unitary channel conductance states. Single channel recordings showed that large unitary conductances (> 200 pS) were generally found between E-E, Fe-Fe, and E-Fe cell pairs, whereas smaller channel sizes (< 90 pS) were detected between R-R cell pairs.