English: This picture is of Dr Robert K. Crane and his sketch on a piece of napkin for coupled cotransport that he proposed at the international meetings in Prague in 1960. The sketch shows brush-border membrane supposedly of the intestinal epithelium showing the digestive surface and the diffusion barrier. During digestion the dietary glucose liberated from sucrose at the digestive surface is transported across the plasma membrane by a sodium-glucose carrier complex. Glucose transport is driven by the inward Na⁺ gradient maintained by the Na⁺ pump. Strophanthidin inhibits the Na⁺ pump causing the Na+ gradient to dissipate and remove the driving force for uphill glucose transport. Phlorizin inhibits cotransport. The model remains valid to this day, apart from some minor details such as the site of phlorizin inhibition (extracellular) and the location of the Na⁺/K⁺ pump.