Effect of caffeine, theophylline and nicotine on D-glucose and folate transport in rat jejunal brush border membrane vesicles.

1. Nicotine at 10 mM, but not caffeine or theophylline, reduced by 20% the overshoot of the Na+-dependent D-glucose transport in rat jejunal brush border membrane vesicles. 2. Since nicotine did not affect the transport of Na+, its inhibition on Na+-dependent D-glucose transport must be due to a direct effect upon the D-glucose transport system. 3. Folate transport in these membrane vesicles was found to a be a free diffusion process at pH 7.4. 4. Neither caffeine, theophylline nor nicotine has any effect on folate transport.