Humoral factors reduce gap junction sensitivity to cytoplasmic pH. II. In vitro manipulations

Our previous studies demonstrated a diurnal rhythm in the response of gap junctions between crayfish giant axons to acidification and that the response was reduced after eyestalk ablation, sinus gland removal, or visual stress. In this paper we describe experiments to test whether compounds in the circulating hemolymph were responsible for modulation of the responsiveness gap junction channels to intracellular pH. In axons from destalked animals in which the hemolymph had been replaced with normal saline, the maximal junctional resistance after acidification (Rjmax) reached control values. In contrast, Rjmax reached only 30% of control after acidification in axons from animals that had been destalked but not perfused. Hemolymph drawn after eyestalk ablation was tested on axons from control animals. Treatment with hemolymph drawn 1 day after destalking resulted in control Rjmax values, while treatment with hemolymph drawn 7 days after destalking resulted in Rjmax values of only 5-40%. Similarly, pretreatment for 1 h with 100 microM ecdysterone resulted in low Rjmax values. These experimental results suggest that a circulating compound, most likely ecdysterone or a related molecule, regulates the physiological properties of gap junctions from crayfish lateral axons.