Submitted to: Toxicologist
Publication Type: Abstract Only
Publication Acceptance Date: 3/1/2002
Publication Date: 3/21/2002
Citation: Riley, R.T., Rentz, S.S., Yoo, H.S. 2002. FUMONISIN B1 (FB1) ALTERS OUABAIN-INSENSITIVE BUT NOT OUABAIN-SENSITIVE 86RB UPTAKE IN LLC-PK1 CELLS WITHOUT ALTERING MEMBRANE PERMEABILITY. Toxicological Sciences. 66:7. Interpretive Summary: Abstract only.
Technical Abstract: FB is a fungal inhibitor of sphingolipid biosynthesis found in corn worldwide. Inhibition of the ceramide synthase causes a dramatic increase in bioactive free sphingoid bases and depletion of glycosphingolipids and sphingomyelin. Studies have shown that free sphingoid bases can modulate Na+/K+ ATPase activity and that altered glycosphingolipid expression can modulate plasma membrane permeability and function. FB also causes lipid peroxidation in rat hepatocytes and cultured cells. The purpose of this study was to determine if FB can alter membrane permeability, Na+/K+ ATPase function, or induce lipid peroxidation in LLC-PK1 cells. Altered membrane ion permeability and Na+/K+ ATPase function was assessed by comparing Rb86 (a transport analog for potassium) efflux and ouabain-sensitive and ouabain-insensitive Rb86 uptake in sub-confluent LLC-PK1 cells exposed to 20 micro-M FB (a minimally cytotoxic concentration) for 72 h. Lipid peroxidation was assessed using the thiobarbituric acid assay in cultures grown under similar conditions but in growth medium without phenol red and at 50 micro-M FB (a cytotoxic concentration). The results show that 20 micro-M FB for 72 h had no effect on Rb86 efflux from Rb86 loaded LLC-PK1 cells nor was there any increase in thiobarbituric acid substances at 50 micro-M. These findings are consistent with the conclusion that under these conditions FB had no effect on membrane permeability. There was also no significant effect on ouabain-sensitive Rb86 uptake indicating that FB had no effect on Na+/K+ ATPase function. There was however a significant inhibition in ouabain-insensitive Rb86 uptake indicating that a minimally cytotoxic but ceramide synthase inhibitory concentration of FB can modify potassium transport processes. A possible target is the ouabain-insensitive phospholipid-dependent Rb86 uptake associated with transporters such as that of the non-gastric H+/K+ ATPase.