A unique striated muscle: further morphological and x-ray microanalytical investigation of the stapedius muscle of the guinea pig using thin and thick cryosections.

Thin (130-200 nm) and thick (10-16 micrometers) cryosections of stapedius muscle of guinea pig were examined by X-ray microanalysis in the scanning- and scanning-transmission mode of electron microscopy. To further explore the unusual elemental composition of stapedius muscle and to evaluate previously used method of analysis of thick cryosections cut at -30 degrees C (Wróblewski et al., 1981), thin cryosections cut at -100 degrees C were investigated. The ultrastructural organisation of stapedius muscle with the centrally located nuclei and the mitochondria could be easily recognized in unstained thin cryosections. X-ray microanalytical investigations of thin sections revealed nearly the same elemental composition of single organelles as results obtained on defined areas in thick cryosections. Analysis of mitochondrial matrix. The elements appeared, however, at the same ratio (1:1). The P/Ca ratio was approximately 6:1 in the nuclei. Myofibrils presented low K and higher Ca concentrations. The levels of other elements (P. S. Cl) were close to those found in the quadriceps muscle of the guinea pig, rat, or human.