PYRIDOXAL 5'-PHOSPHATE RELATED CHANGES IN RETENTION OF 1,25-DIHYDROXYVITAMIN-D-RECEPTOR LIGANDS IN RAT INTESTINAL-MUCOSA CELL-NUCLEI

After feeding rats a vitamin B-6-deficient diet, we observed a decreas e in pyridoxal 5'-phosphate concentrations in intestinal mucosa cells to 32 and 48% of control in cytoplasm and cell nuclei, respectively. C orrelation analysis suggested that there were two pyridoxal 5'-phospha te pools in the nuclei: a ''mobile'' pool (equivalent to about 5% the concentration of the cytoplasmic pyridoxal 5'-phosphate), and a ''stab le'' pool, which was independent of cytoplasmic fluctuations of pyrido xal 5'-phosphate (about 9 pmol pyridoxal 5'-phosphate/mg DNA). Reducti on in pyridoxal 5'-phosphate content in the cells of vitamin B-6-defic ient animals was accompanied by a substantial increase in 1,25-dihydro xyvitamin D-receptor ligand concentration in the cell nuclei (76.6+/-1 9.7 vs 762 +/- 291. fmol/mg DNA, mean +/- SEM). The degree of 1,25-dih ydroxyvitamin D accumulation in the nuclei appeared to be an exponenti al function of the ''mobile'' nuclear pyridoxal 5'-phosphate concentra tion. Semilogarithmic transformation of the data yielded a straight li ne, representing an inverse correlation between the cytoplasm-related nuclear pool of pyridoxal 5'-phosphate and the logarithm of the 1,25-d ihydroxyvitamin D concentration in the nuclei (r = -0.95). These data suggest that pyridoxal 5'-phosphate may be related to 1,25-dihydroxyvi tamin D retention in the nuclei, possibly through interaction of the p yridoxal 5'-phosphate with the vitamin D receptor protein in the nucle i.