Muscle spindle afferents and the mystery of the alpha3 isoform of Na+,K+-ATPase.

摘要

Normal nervous system function is critically dependent upon Na~+,K~+-ATPase activity. The functional Na~+,K~+-ATPase, a complex of alpha, beta and gamma protein subunits, hydrolyses ATP to exchange intracellular Na~+ for extracellular K~+. Thus, the transporter sets and maintains Na~+ and K~+ gradients controlling the resting membrane potential and neuronal excitability. Because of unequal exchange of K~+ for Na~+, Na~+,K~+-ATPase is an electrogenic mechanism that adds to the generation of hyperpolarizing afterpotentials when activated, thus modulating the frequency and duration of neuronal discharges. The Na~+,K~+-ATPase is the major mechanism preventing extracellular accumulation of K~+ and associated hyperactivity of neuronal networks and centres. Despite such profound involvement in basic nervous function, many aspects of active ion transport by Na~+,K~+-ATPase within the nervous system are poorly understood. One unresolved matter concerns neuronspecific expression of the alpha_3 isoform of the Na~+,K~+-ATPase (Dobretsov & Stimers, 2005).