Laser Raman study of internally perfused muscle fibers. Effect of Mg2+, ATP and Ca2+.

Raman spectra of an intact muscle fiber and of internally perfused fibers in capillary tubes have been obtained. The use of internal perfusion has insured a good control of the concentration of Ca2+, Mg2+ and ATP. The comparison of the spectra obtained with the two types of fibers shows that the muscle structure is well preserved in capillary tubes. In addition, it appears that the sarcomere length has no significant effect on the Raman spectrum of muscle fibers. Our results on perfused fibers demonstrate that a fiber can be kept in the relaxed state for several hours, then displaying an intact fiber spectrum, when the concentration of ATP, Mg2+ and Ca2+ is maintained at 5, 2 and 0 mM, respectively. Therefore ATP and Mg2+ do not affect the Raman spectrum of muscle fibers. When one of these components is removed, or when Ca2+ is added, contraction occurs and causes major spectral changes. These results are interpreted as being due to strong electrostatic interactions between basic and acidic residues during contraction, and to a change of the alpha-helical content, or of the orientation, of some of the contractile proteins.