MEMBRANE-TRANSPORT OF NEURONAL NITRIC-OXIDE SYNTHASE SUBSTRATE L-ARGININE IS CONSTITUTIVELY EXPRESSED WITH CAT1 AND 4F2HC, BUT NOT CAT2 OR RBAT

The potential induction of cationic and zwitterionic amino acid transp ort systems and mRNA transcripts was investigated in primary neuronal cultures from rat hypothalamus/brainstem. Cultures exposed to bacteria l lipopolysaccharide (LPS) plus interferon-gamma (IFN gamma) were asse ssed with respect to northern blot analyses, L-leucine/L-arginine cros s-inhibition uptake profiles in the presence and absence of Na+, and i nitial rate sodium-independent L-arginine transport kinetics. L-Argini ne uptake activity was constitutively expressed along with uninduced s teady-state levels of CAT1 and 4F2hc transcripts. However, neither the high-affinity nor the low-affinity alternatively spliced inducible is oforms of CAT2 or CAT2a transcripts (encoding system y(+) in control a strocytes, lymphocytes, or liver) nor the rBAT transcripts (encoding s ystem b(0.+) in control intestinal epithelial cells) were detected by northern analysis of neuronal mRNA. Cross-inhibition profiles were con sistent with physiologic system y(+) activity, but not system b(0,+) o r system y(+)L. Transport kinetics gave a single component with V-max = 113 +/- 7 pmol/min/mg of protein and K-m = 47 +/- 8 mu M L-arginine; these kinetic parameters were not influenced by addition of LPS/IFN g amma at concentrations that up-regulated CAT2 mRNA and system y+ activ ity in control astroglia from the same area of the brain. The data are consistent with L-arginine membrane uptake occurring via only system Y+ encoded by constitutive CAT1, with possible physiologic contributio n by constitutive 4F2hc transcripts in primary neuronal cultures.