Humoral factors reduce gap junction sensitivity to cytoplasmic pH. I. Organ ablation studies

The sensitivity of gap junctions connecting crayfish lateral axons to uncoupling by axoplasmic acidification was studied after altering the hormonal balance of animals by 1) ablation of eyestalks or sinus glands or 2) inducing long-lasting defensive posturing behavior (stress). Internal pH (pH(i)) was measured with microelectrodes, and junctional resistance (R(j)) was calculated from input and transfer resistances. In isolated nerve cords from intact animals, the maximal R(j) (R(jmax)) reached after acidification varied diurnally (R(jmax) ~10 and 0.6 MΩ at 0900 and 1800 h, respectively). Basal R(j) (20-30 kΩ) did not change during the 24-h period. Organ ablation (eyestalks or sinus glands) or stress rendered gap junctions less sensitive to uncoupling by low pH(i) within 1 h or 2 days; recovery toward control values had different time courses. The reduced pH sensitivity of crayfish junctions seen after eyestalk ablation is attributable to stress in its early phase (lasting 1-2 days) and to ablation of the endocrine organs in its late phase (2-7 days). No striking structural differences accompanied these changes, indicating that the altered properties are not due to major changes in gap junction expression.