Activity of the Extrinsic and Intrinsic Muscle Networks of the Malpighian Tubules and the Ureter in the Female Stable Fly, Stomoxys calcitrans (L.)

Abstract

The four Malpighian tubules observed in the female stable fly, Stomoxys calcitrans (L.), are divided into an anterior dorsal pair and a posterior ventral pair. Intrinsic muscles were found only in the short proximal section (ureter) of each pair of tubules that emptied into the midgut. Isolated preparations of the ureter demonstrated four types of organized rhythmic activity: compression, peristalsis, reverse peristalsis, and segmentation. Compression caused a momentary (0.4 to 0.6 sec) shortening of the longitudinal muscle fibers in a localized region of the ureter. Peristalsis was the dominant type of activity. Each wave progressed along the duct with a duration that ranged from 0.9 to 1.7 sec. Segmentation consisted of a localized annular constriction of the ureter without progression that lasted for a duration of 0.3 to 0.6 sec. The large distal ends of the dorsal pair of tubules showed spontaneous movement in situ. Close examination revealed a network of extrinsic muscle cells attached to the distal tubular ends. The motile properties of the extrinsic muscles were slower and not as complex as those of the ureter. The sequence from the resting state to contraction and return was much longer with durations that ranged from 10.8 to 27.1 sec. Also, the time for peak tension was 5 to 25.9 sec in duration. The extrinsic muscles did not show the organized and rhythmic activity observed in the ureter.