Deprival of nicotinamide leads to enhanced glucose transport in chick embryo fibroblasts.

Chick embryo fibroblasts growing in medium free of pyridine ring precursors of NADH and NADPH replicate several times before multiplication ceases. The rate of glucose transport is progressively enhanced, finally reaching levels several times higher than those normally observed in cells severely depleted of NADH. Whereas normal cells respond to additional glucose by further reducing transport, the NADH-depleted cell is refractory to glucose even at five times the normal glucose concentration. Readdition of nicotinamide does little to restore normal transport within 24 h. On the other hand NAD+ or NADP+ provided simultaneously with glucose results in a sharp decline in measurable transport within 2-4 h. The role of the pyridine nucleotides in this reduction of transport function is for the moment unknown.