Glucose availability and the electrophysiology of the human visual system.

Glucose is a main energy source to neurons in brain (with limited storage capability) and retina (where it is stored in glial Müller cells and supplied upon demand). Glucose availability and visual function are related. Human positron emission tomography studies indicate increased blood flow and glucose metabolic rate in primary visual cortex during stimulation, with retinotopic distribution. Retinal electrophysiology covaries with glucose concentration in in vitro models as well as in humans, at comparable concentrations in the physiological range. The interactions between retinal electrophysiology (notably the electroretinogram b-wave) and glucose metabolism appear more stringent than for cortical evoked responses. K-channels regulated by intracellular ATP are thought to link neuron excitability (and electrophysiological activity) on the metabolic state. High-affinity sulphonylurea binding sites for K-channels are widely distributed in brain. K-channels conceivably modulate neurotransmitter release and are inactivated by elevated glucose concentrations and sulfonylurea drugs used to treat diabetes.