Glucose uptake in porcine carotid artery: Relation to alterations in active Na⁺-K⁺ transport

In vascular smooth muscle (VSM), aerobic lactate production can account for as much as 30% of the basal rate of ATP production. Generally, glucose transport is thought to be the rate-limiting step for glycolysis in unstimulated VSM. In this work we provide evidence that the intracellular concentration of glucose is negligible in porcine carotid artery, indicating that glucose transport is rate limiting for its utilization. Since aerobic glycolysis appears to be coupled to active Na⁺-K⁺ transport in this tissue, we examined the effects of altering ion transport on glucose transport. Glucose uptake and 3-O-methyl-D-glucose transport were accelerated, though intracellular glucose remained negligible in artery rings that were incubated with 80 mM KCl, which is known to stimulate active Na⁺-K⁺ transport, as well as aerobic glycolysis and mechanical activity. On the other hand, inhibitors of active Na⁺-K⁺ transport (ouabain, Na⁺-free media), which also elicit mechanical activity, had little effect on sugar transport but significantly inhibited aerobic glycolysis and caused an intracellular accumulation of glucose. Our results indicate the following: 1) that glucose transport is regulated in VSM; 2) that the intracellular concentration of Ca²⁺ does not appear to regulate sugar transport, since changes in glucose and 3-O-methyl-D-glucose transport are not always seen in association with increased mechanical activity, and 3) that the decrease in aerobic glycolysis associated with the inhibition of active Na⁺-K⁺ transport is not due to a decrease in glucose transport but rather to an inhibition of glucose utilization.