A standing Na+ conductance in rat carotid body type I cells

Substitution of extracellular Na+ with N-methyl D-glucamine caused marked h yperpolarisation in rat isolated carotid body type I cells,suggesting the p resence of a standing Na+ conductance. Choline substitution produced smalle r hyperpolarisations, whilst Li+ was virtually without effect. This Na+ con ductance was not blocked by amiloride, tetrodotoxin, Zn2+ or Gd3+ and did n ot arise from electrogenic Na-glucose cotransport, since substitution of gl ucose with sucrose could not mimic the effects of Naf substitution. Hypoxia and acidosis did not modify the tonic Na+ influx. Our results suggest that Na+ influx provides a constant depolarising influence on type I cells whic h acts to shift membrane potential beyond that required for initiation of n eurosecretion, an essential step in carotid body chemotransduction. NeuroRe port 12:1421-1425 (C) 2001 Lippincott Williams & Wilkins.