d-Glucose transport across the apical membrane of the surface epithelium inNereis diversicolor

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Abstract
Epidermald-glucose transport was investigatedin vivo in the brackishwater polychaete wormNereis diversicolor. Transfer across the apical membrane is rate-limiting tod-glucose uptake, but the cuticle and/or mucus presents some resistance tod-glucose diffusion between bulk solution and transporting membrane. Maximald-glucose influx is about 10−12 mol sec−1 per cm2 of apical plasmalemma. Under natural conditions (∼1 μm d-glucose in the medium), backflux from the epidermal transport pool is negligible, but a significant paracellular outflux may occur.d-glucose influx across the apical membrane is Na+-dependent and completely inhibitable by phlorizin and harmaline; phloretin is less effective, and cytochalasin B has no effect. Influx is moderately depressed by KCN and iodoacetate. α-methyl-d-glucopyranoside is an effective substitute ofd-glucose in transport. Animals acclimated to a low salinity, in which epidermal salt transport takes place, show a marked decrease ofd-glucose transport capacity. On transfer of animals from a high to a low salinity, or vice versa, the corresponding change of influx occurs after a time-lag of at least an hour. Permeability of the epidermis to simple diffusion ofd-glucose is 8×10−8 cm sec−1 (on basis of gross epidermal area).