Comparison of the lateral diffusion coefficient of hepatocyte plasma membrane proteins in three strains of sensescence accelerated mouse (SAM)

The lateral diffusion coefficients of proteins (Dp) were measured in hepatocyte plasma membrane in freshly prepared liver smears by means of the fluorescence recovery after photobleaching (FRAP) method. Dp was measured after development of peroxide-induced autofluorescence (PIAF) in a total of 115 senescence accelerated mice (SAM), distributed in three strains, at least five age-groups in each, as follows: (i) SAMR1TA (25 males and 22 females), medium life span (MLS) in months, under specific pathogen free (SPF) conditions, MLSspf 20.1 and 20.0, respectively, while under conventional conditions, MLSΔpf=18.9 in average for both sexes; (ii) SAMP6/Ta (18 males and 17 females), MLSspf=17.1 and 15.3, respectively, and MLScc=8.1 for both sexes; (iii) SAMP6/Ta (17 males and 16 females), MLSspf=15.6 and 14.7, respectively, and MLScc=10.0 for both sexes. A highly significant negative linear age-correlation of Dp (R=0.975 or higher) was found in each strain, being roughly proportional with the MLScc values. Since the studied mice kept under SPF conditions survived longer, than under conventional conditions, the actual age-dependent decay rates of Dp values did not differ significantly in two pairs of comparisons (female R1/P6 and female R1/P8), whereas they did in all other possible pairs, including also the normal C57BL/6 mice. The main conclusion can be drawn that the Dp of hepatocyte membranes is a good biomarker of aging and survival also in SAM, as in all other inbred and outbred rodents, studied so far.