DISTRIBUTION OF SODIUM, MAGNESIUM, CHLORINE, CALCIUM, POTASSIUM, PHOSPHORUS AND SULFUR IN Z-BANDS, I-BANDS AND A-BANDS IN MAMMALIAN STRIATED-MUSCLE

The regularity of the striation of skeletal muscle offers a unique pos sibility to analyze different bands of the sarcomere in longitudinally cut semithin cryosections. The aim of the present study was to invest igate the elemental content of the Z-, I- and A-bands within the sarco mere which may be related to the affinity of an element to different c ontractile elements and the water content in different bands. The high est potassium levels were found in the Z-band {802 mmol/kg dry weight (d.w.)} as compared to the I-band (697 mmol/kg d.w.) and the A-band (7 31 mmol/kg d.w.). The difference between A-band and Z-band, but not be tween I-band and A-band, was significant. The highest phosphorus value s were detected in the Z- and I- bands and the lowest within the A-ban ds (632, 615 and 540 mmol/kg d.w. respectively). No significant differ ences were found in the concentrations of Na, S, or CI. Ca was signifi cantly lower in the I-band as compared to A- and Z-band. The Mg concen tration in the I- and A-band was significantly higher than in the Z-ba nd. By means of computerized densitometry, relative densities (proport ional to the dry mass content) of the Z-, I- and A-band were calculate d (23.9, 11.6, and 19.2, respectively). The mean value of dry mass ove r several sarcomeres varied between 19.5-22.5 which corresponds well w ith dry weight mass concentrations obtained by traditional methods. Th e values for dry mass content allowed recalculation of the elemental c oncentrations as mmol/kg wet weight.