The use of ionic lanthanum as a diffusion tracer and as a marker of calcium binding sites.

The distribution of ionic lanthanum (La3+) was studied after perfusion of the isolated rat heart with a buffered salt solution containing lanthanum chloride. We have demonstrated that the localization of lanthanum differed from that shown in previous studies in which hearts were exposed to ionic or colloidal lanthanum during or after fixation. La3+ passed rapidly through the intercellular cleft between endothelial cells. There was relatively little transport by micropinocytosis and no evidence of transendothelial passage through the cytoplasm. Perfusion with a solution containing 1 to 15 mM LaCl3 resulted in localization of La3+ on the entire cytoplasmic membrane system of muscle cells, i.e.: the non-specialized parts of the muscle cell membranes were stained by La3+ as well as the membranes of micropinocytotic vesicles, of the T-system and of the intercalated disc. The cytoplasmic leaflets of gap junctions were especially stained. However, the cell membranes of non-muscle cells were free of lanthanum precipitates. Freeze-fracturing of muscle cells showed concomitant alteration in the distribution of membrane-associated particles. The gap junction membranes also showed changes in particle aggregation. Intracellular binding of La3+ are restricted to muscle cells. Lanthanum was found in the cell nucleus associated with heterochromatin, in the nucleolus, and along the nuclear membrane. The myofibrils were stained mainly over the I-band.

[Ultrastructure of the vocal muscle and its morphological differences from the myocardium]. / Die Ultrastruktur des Musculus Vocalis und seine morphologischen Unterschiede zur Herzmuskulatur

A comparative ultrastructural investigation of the M. vocalis in mammals has been carried out. Morphological differences between the vocal muscle and cardiac tissue are reported; a distinct classification of the M. vocalis according to a typisation of skeletal muscle fibers is presented. In all species investigated (man, dog, cat, guinea-pig and rat) the general ultrastructure of the sarcomeres as well as their mitochondrial content and the innervation pattern allow to classify the M. vocalis as to belong to the "fast twitch (white) skeletal muscle fibers. A single innervation was found with large motor endplates containing numerous synaptic infoldings. Structural specializations known to be characteristic for cardiac tissue, e.g. intercalated discs, T-tubules at the level of the Z-band and nuclei in a midst postion of the muscle cell could not be observed. The m. vocalis, therefore, cannot be considered to have histologically any relationship with cardiac tissue. The vocal muscle is described as a special type of skeletal muscle very similar to the extraocular muscles. The electron microscopic findings are discussed with respect to current theories of phonation. The myoleastic theory of phonation can be favoured according to our ultrastructural results.