This study was designed to quantify nitric oxide synthase (NOS) activity in
microdissected glomeruli (Glm), pars convoluta, pars recta, cortical colle
cting duct, cortical thick ascending limb, outer medullary collecting duct,
medullary thick ascending limb and thin limb, inner medullary collecting d
uct (IMCD) and thin limb, and vasa recta (VR). Total protein from microdiss
ected segments was incubated with L-[H-3]arginine and appropriate cofactors
, and the L-arginine and converted L-citrulline were separated by reverse-p
hase HPLC and radiochemically quantitated. NOS activity was found to be gre
atest in IMCD (11.5 +/- 1.0 fmol citrulline mm(-1) h(-1)) and moderate in G
lm (1.9 +/- 3 fmol.glomerulus(-1)h(-1)) and VR (3.2 +/- 0.8 fmol mm-l h-l).
All other renal structures studied exhibited significantly less NOS activi
ty. The mRNA for NOS isoforms in the NOS activity-positive segments was the
n identified by RT-PCR. The IMCD contained mRNA for neuronal (nNOS), endoth
elial (eNOS), and inducible NOS (iNOS), but Glm and VR only expressed the m
RNA for nNOS and eNOS. These experiments demonstrate that the greatest enzy
matic activity for NO production in the kidney is in the IMCD, three- to si
xfold less activity is present in the Glm and VR, and minimal NOS activity
is found in other segments studied.