L-GLUTAMINE AND L-ASPARAGINE STIMULATE NA-H+ EXCHANGE IN PORCINE JEJUNAL ENTEROCYTES()

L-Glutamine (Gin) is a major respiratory fuel and substrate for nuclei c acid synthesis in mammalian intestinal cells. The structurally relat ed amino acid, L-asparagine (Asn), stimulates the proliferative enzyme ornithine decarboxylase in colonocytes, an effect that is blocked by the Na+-H+ exchange inhibitor amiloride. In an epithelial cell line de rived from newborn piglet jejunum (IPEC-JB cells), we determined intra cellular pH (pH(i)) by computer-assisted microfluorimetry in single ce lls loaded with pH-sensitive dye 2',7'-bis(2-carboxyethyl)-5(6)-carbox yfluorescein. Resting pH(i) in N-2-hydroxyethylpiperazine-N'-2-ethanes ulfonic acid-buffered NaCl Ringer was 7.06 +/- 0.02. Removal of extern al Na+ caused reversible acidification; recovery of pH(i) from NH4+-in duced acid load was Na+ dependent, amiloride inhibitable, and Cl- inde pendent. Asn and Gin had no measurable effect on resting pH(i), but pr etreatment with Asn or Gin induced a consistent twofold increase in pH (i) recovery from an acid challenge that was not seen with L-proline, D-glutamine, or L-phenylalanine. Inhibition of Gin metabolism by amino oxyacetate abolished the stimulatory effect of Gin on the exchanger. T he tumor promotor phorbol 12-myristate 13-acetate (PMA) stimulated rec overy rate from acid load and also increased resting pH(i). The effect s of PMA and Gin on Na+-H+ exchange from acid load were additive. Stim ulation of Na+-H+ exchange by PMA, but not by Gin, was inhibited by pr otein kinase C (PKC) inhibitor 1-(5-isoquinolinylsulfonyl)-2-methylpip erazine. We conclude that Gin metabolism stimulates Na+-H+ exchange of acid-loaded porcine enterocytes by a mechanism not requiring activati on of PKC.