ACETYL COA-ARYLAMINE N-ACETYLTRANSFERASE ACTIVITY IN RAT HEPATOCYTES CULTURED ON DIFFERENT EXTRACELLULAR MATRICES

N-Acetyltransferase (NAT) activity towards p-aminobenzoic acid and sul famethazine was examined in primary cultures of rat hepatocytes cultur ed on three extracellular matrices (ECM)-type I collagen, thermally de natured type I collagen, and Matrigel(R). Whereas protein and DNA cont ent declined markedly during the first 24 hr of culture, p-acetylamido benzoate (AcPABA) and N-acetylsulfamethazine (AcSMZ) formation were re adily detectable on all three ECM for the 6-day culture period. Protei n and DNA content, as well as NAT activities, were higher on Matrigel than on either of the other two ECM. Additional studies were conducted to confirm the expression of both enzymes during the culture period. The ratio of AcPABA to AcSMZ formation remained relatively stable thro ughout the 6-day culture period, suggesting that both enzymes continue d to be expressed throughout the study period. Further studies in cell s cultured on Matrigel revealed that AcPABA formation exhibited a time -dependent decline when cytosol from cultured cells was incubated at 5 0 degrees C, whereas AcSMZ formation proved to be thermostable. Moreov er, methotrexate substantially inhibited AcPABA formation, but had onl y modest effects on AcSMZ. These studies support the conclusion that A cPABA and AcSMZ are predominantly formed by way of different enzymes t hroughout the culture period. These findings are supported by the obse rvation that NAT1 and NAT2 mRNA were detectable on all days examined. These data indicate that primary cultures of rat hepatocytes should pr ove useful in probing the regulation of NAT and its role in toxicity. (C) 1997 Elsevier Science Ltd.