Charge-Dependent Molecular Movement Through Intercellular Bridges in Drosophila Follicles

The steady-state membrane potentials of the nurse cells of Drosophila melanogaster incubated in a Ringer's solution containing 2.5 mM K⁺ averaged 5.2 mV more negative than those of oocytes to which they were attached by intercellular bridges (n = 159; P < 0.001, paired t-test). In sodium azide, the resting potentials of the two cells diminished from a range of -50 to -70 mV to an average of -10 mV, and the transbridge difference disappeared. Therefore, the transbridge difference is dependent upon metabolic energy. Lucifer yellow CH, when microinjected into either nurse cells or oocytes, became distributed in less than 30 min in a manner to be expected for a negatively charged fluorochrome in an electrically polarized system. Polarity was even more striking in this study than reported earlier for Drosophila follicles incubated in a higher K⁺ medium (Woodruff et al., 1988).