Inflow and outflow times of Lucifer yellow in proximal tubules after lipopolysaccharide injection. The inflow time, which reflects glomerular filtration rate, was determined by how quickly Lucifer yellow appeared and reached the peak concentration in the proximal tubules after the injection. Five spatially dissociated proximal tubules that showed Lucifer yellow right after the injection were employed to count the inflow time. The inflow time of Lucifer yellow was similar in floxed control and proximal tubular guanylyl cyclase A knockout (pGC-A-KO) mice, with and without human recombinant arterial natriuretic peptide (ANP; n = 22 to 25 tubules in 5 mice). The outflow time reflects the washout of tubular fluid from proximal tubules to downstream nephron. The outflow time was analyzed in the nephrons that were used for the inflow time analysis, and was defined as the time from peak to half peak of fluorescence intensity. The outflow time of Lucifer yellow was prolonged in the floxed control mice, and this was shortened by human recombinant ANP treatment. The effect of human recombinant ANP was not significant in pGC-A-KO mice.