Bundles Of Myofibrils Research Articles

Fine structure of Dirofilaria immitis body-wall musculature

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.

Natural photosensitivity of Spirographis muscle

In connexion with the study of the factors affecting the rhythmical movements of marine invertebrates, the spontaneous photosensitivity of Spirographis muscles has been observed. The physiological characteristics of muscle stimulation in this annelid can be summarized as follows: 1. 1. The spontaneous rhythm of the muscular contractions shows phases of intense activity and phases of absolute repose. Stimulation by light during the phase of activity causes complete blockage of the contractions, while stimulation during the rest phase evokes contractions. 2. 2. The amplitude of the contractions increases proportionally with the increase in surface area of muscle exposed to light. 3. 3. The duration of muscle block induced by exposure to light is directly proportional to the logarithm of the intensity. 4. 4. If the intensity of the illumination is sub-threshold, no excitation is observed even if the exposure is long. However, increase in the amplitude of contractions of the isolated myofibril bundles is observed with progressive increase of intensity. Furthermore, an optimum intensity has been observed, after which the response diminishes. 5. 5. As in the case of electric stimulation, the muscle of Spirographis shows a refractory phase during which it is not responsive to stimulation by light. 6. 6. The Spirographis muscle responds to light spread over the whole visible spectrum but preferentially absorbs radiations of wave lengths ranging from 5000 to 6500 Å. The experimental data reported here are not sufficient to allow a definite conclusion as to the mechanism of muscle photostimulation in Spirographis. However, it seems probable that the effective fraction of the spectrum acts on pigment pre-existing in the myofibril.