Fine structure of Dirofilaria immitis body-wall musculature

Abstract

The somatic muscle of Dirofilaria immitis is composed of individual fusiform cells consisting of a myofibrillar and an amyofibrillar portion. The cells are separated by material continuous with the basement membrane and have sarcolemmal, but not sarcoplasmic, connections at both myofibrillar and an amyofibrillar portions. Thick and thin myofilaments make up the bundles of myofibrils. They are inter-laminated obliquely at regular intervals by interfibrillar structures. This arrangement causes the appearance of oblique striation. The interfibrillar structures are penetrated by sarcotubules, and contain fibrous elements, dense bodies often associated with sarcotubular membranes, numerous mitochondria, and single and compound glycogen particles. The present findings basically agree with those recently reported for Ascaris lumbricoides muscle, but differ by the presence of glycogen and mitochondria in the interfibrillar areas, the presence of tight junction between myofibrillar portions of adjacent cells, and the absence of a sarcoplasmic core in the myofibrillar portions.