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

L-Glutamine (Gin) is a major respiratory fuel and substrate for nucleic acid synthesis in mammalian intestinal cells. The structurally related 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 derived from newborn piglet jejunum (IPEC-JB cells), we determined intracellular pH (pH(i)) by computer-assisted microfluorimetry in single cells loaded with pH-sensitive dye 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein. Resting pH(i) in N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid-buffered NaCl Ringer was 7.06 +/- 0.02. Removal of external Na+ caused reversible acidification; recovery of pH(i) from NH4+-induced acid load was Na+ dependent, amiloride inhibitable, and Cl- independent. Asn and Gin had no measurable effect on resting pH(i), but pretreatment 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 aminooxyacetate abolished the stimulatory effect of Gin on the exchanger. The tumor promotor phorbol 12-myristate 13-acetate (PMA) stimulated recovery rate from acid load and also increased resting pH(i). The effects of PMA and Gin on Na+-H+ exchange from acid load were additive. Stimulation of Na+-H+ exchange by PMA, but not by Gin, was inhibited by protein kinase C (PKC) inhibitor 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine. We conclude that Gin metabolism stimulates Na+-H+ exchange of acid-loaded porcine enterocytes by a mechanism not requiring activation of PKC.