LONGITUDINAL BODY-WALL MUSCLES ARE ELECTRICALLY COUPLED ACROSS THE SEGMENTAL BOUNDARY IN THE 3RD INSTAR LARVA OF DROSOPHILA-MELANOGASTER

Longitudinal body wall muscles in the third instar larva of the fruitf ly, Drosophila melanogaster, were systematically examined for electric al and dye coupling. These muscle cells were found to be electrically coupled but rarely dye-coupled across the segmental boundary. The inte r-segmental coupling coefficients between muscle #6s and muscle #7s ac ross the segmental boundary were 0.33 +/- 0.09 (mean +/- S.D., n = 12) and 0.43 +/- 0.09 (n = 5), respectively, which are much larger than v alues previously reported in Drosophila but similar to those reported in the blowfly and hawkmoth. By contrast, the intra-segmental coupling coefficient between muscles #6 and #7 was smaller, 0.16 +/- 0.08 (n = 28). Other muscle cells which had apparent physical contacts with the se longitudinal muscles were examined bur. were nor electrically coupl ed to them. Nerve-evoked as well as miniature excitatory junctional po tentials were found also electrotonically spread across the segmental boundary. The inter-segmental coupling between muscle #6s was not bloc ked by the gap junction inhibitors halothane or l-octanol. Functional significance of this electrical coupling is apparently in coordination of larval body movements.