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Liver carnitine palmitoyl transferase (L-CPT) I is a key regulatory enzyme of long-chain fatty acid (LCFA) oxidation that ensures the first step of LCFA import into the mitochondrial matrix. In rat hepatocytes, we showed previously that L-CPT I gene expression was induced by LCFAs as well as by fibrates. The aim of this study was to determine whether LCFA-induced L-CPT I gene expression was mediated by PPAR[alpha]. For this purpose, we constructed a PPAR[alpha]-dominant negative receptor to inhibit endogenous PPAR[alpha] signaling. Highly conserved hydrophobic and charged residues ([Leu.sup.459] and [Glu.sup.462]) in helix 12 of the ligand-binding domain were mutated to alanine. These mutations led to a total loss of transcriptional activity due to impaired coactivator recruitment. Furthermore, competition studies confirmed that the mutated PPAR[alpha] receptor abolished the wild-type PPAR[alpha] receptor action and thus acted as a powerful dominant negative receptor. When overexpressed in rat hepatoma cells (H4IIE) using a recombinant adenovirus, the mutated PPAR[alpha] receptor antagonized the clofibrate-induced L-CPT I gene expression, whereas it did not affect LCFA-induced L-CPT I. These results provide the first direct demonstration that LCFAs regulate L-CPT I transcription through a PPAR[alpha]-independent pathway, at least in hepatoma cells. KEY WORDS: * dominant negative PPAR[alpha] * recombinant adenovirus * carnitine palmitoyl transferase I * hepatoma cell * fatty acid-induced gene expression

Studies on chloride transport across basolateral membrane (BLM) reveal the presence of two different pathways for chloride uptake across guinea pig jejunal BLM, a rheogenic conductance mechanism and a chloride-chloride exchange. The chloride-chloride stoichiometry is variable, as indicated by the breakability of the exchange into electroneutral and rheogenic components. The additivity of conductance and exchange activities indicate distinct molecular bases for the two mechanisms.