VOLTAGE-DEPENDENT GAP JUNCTIONAL CONDUCTANCE IN HEPATOPANCREATIC CELLS OF PROCAMBARUS-CLARKII

Properties of gap junction channels present between specific cell type s 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 bas is of their morphology using light and electron microscopy. Although j unctional conductance (G(j)) 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 (V-i-0), such that G (j) increased with hyperpolarization to a maximal plateau reached at a pproximately - 40 mV and was abolished with depolarization > 10 mV. Th e G(j)-V-i-0 relationship can be described by a squared Boltzmann rela tion with A = 0.101 and V-0 = 0.135 mV. In this system, sensitivity of the junctions to transjunctional voltage was slight, if present at al l. Gating mechanisms were complex, as evidenced by the presence of mul tiple unitary channel conductance states. Single channel recordings sh owed that large unitary conductances (> 200 pS) were generally found b etween E-E, Fe-Fe, and E-Fe cell pairs, whereas smaller channel sizes (< 90 pS) were detected between R-R cell pairs.