The hepatic uptake of a hydrophilic, cationic linear
peptide with
renin inhibitory activity [5(4-amino-piperidyl-1-carbonyl)-L-2,6[3H]phenyl-alanyl-beta-alanyl-(4S- amino-3S-hydroxy-5-cyclohexyl)-pentan-carbonyl-L-isoleucyl-amin ome thyl-4-amino-2-methyl-
pyrimidine-citrat] (code number
EMD 56133; EMD, E. Merck, Darmstadt) was investigated in isolated rat hepatocytes.
EMD 56133 was taken up by isolated rat liver cells in a time-, concentration-, energy- and temperature-dependent manner. The uptake was a combination of diffusion and a carrier-mediated process.
EMD 56133 was accumulated 4.5-fold in liver cells. Eighty-three per cent of the accumulated
peptide was found in the cytosol, not bound to
membrane proteins. Seventeen per cent was associated with
membrane proteins after cell fractionation and centrifugation at 100,000 g. The permeability coefficient of the non-saturable uptake of
EMD 56133 was P = 1.973 x 10(-6) cm/sec. The kinetic constants for the carrier-mediated transport are Km = 92 microM and Vmax = 128 pmol/mg x min. Various substrate analogs inhibited the uptake of
EMD 56133. AS-30D
ascites hepatoma cells and Reuber
hepatoma cells did not accumulate
EMD 56133. The absence of
oxygen or a decreased cellular
ATP content blocked the hepatocellular uptake of the
renin inhibitor. Temperatures above 20 degrees increased the transport; the activation energy was determined to be Aapp = 41 kJ/mol. The apparently active uptake of
EMD 56133 was not
sodium dependent. In contrast, the membrane potential might be a driving force for the transport of the positively charged
EMD 56133.