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The membrane transport of 3-O-methyl-D-glucose was studied in vitro in a smooth muscle, the detrusor of rat urinary bladder. Transport occurred by facilitated diffusion and showed the same chemical specificity and sensitivity to specific inhibitors as skeletal and cardiac muscle but its insulin sensitivity was smaller. Transport was increased by agents inhibiting the Na+pump and was decreased by agents which increased Na+ and K+ gradients by apparently stimulating the Na+pump. In accord with a rate limiting role of transport in glucose utilization, similar stimulating and inhibitory effects were seen when CO2 production from (14C) glucose was measured.

The mode of absorption of L-glucose and D-xylose was studied in vitro in preparations of hamster small intestine. Both sugars were actively transported from the lumen into the tissue when present at low concentrations. Their transport was Na+-dependent and was inhibited by ouabain, phlorizin, and competing sugars. Vmax for both sugars was Na+-independent and identical with that for many other monosaccharides. The apparent Km was only 5 times (D-xylose) or 8 times (L-glucose) less in the presence than in the absence of Na+(in contrast to 130 times for D-galactose). This explains why active transport is limited in extent and observable only at low concentrations. Countertransport was demonstrated with both these weakly transported sugars in the presence of strongly transported sugars, e.g. D-glucose, which explains the apparent secretion of L-glucose in the kidney in vivo. It is concluded that the mode of transport of L-glucose and D-xylose is identical with that of other sugars and consistent with a model proposed earlier.