CONTRIBUTION OF THE MITOCHONDRIAL COMPARTMENT TO THE OPTICAL-PROPERTIES OF THE RAT-LIVER - A THEORETICAL AND PRACTICAL APPROACH

The purpose of this work was to analyze the contribution of the mitoch ondria to the optical properties, i.e., light absorption and scatterin g, of the blood-free rat liver. Firstly, a theoretical model of the re duced scattering coefficient of the liver was performed by using the M ie theory, the Rayleigh-Debye-Gans approximation, and the electron mic roscopy descriptions of the liver ultrastructure. Compared with the he patocyte volume, the nucleus and the peroxisomes, the mitochondria com partment, accounting for 22% of the liver cell volume, seemed to be th e predominant factor for the light scattering of the liver. Second, by using time-resolved spectroscopy and a sample substitution method, we have measured the absorption and reduced scattering coefficients of b lood-free perfused rat livers, isolated hepatocyte suspensions, and is olated mitochondria suspensions. A subsequent extrapolation of the iso lated mitochondria data to the in vivo mitochondrial content and a com parison with the whole liver measurements lead to the following conclu sions: 1) the mitochondria account for about 50% of the liver absorpti on coefficient at 780 nm (mu(a) = 0.25 cm(-1) extrapolated from isolat ed mitochondria vs. 0.53 +/- 0.05 cm(-1) measured for the liver); and 2) the mitochondrial compartment is the primary factor for the light s cattering in the rat liver (mu(s)' = 15.5 cm(-1) extrapolated from the isolated mitochondria versus 15.9 +/- 2.4 cm(-1) measured for the liv er), demonstrating the relevancy of our preliminary theoretical study.