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pubmed:abstractText |
1. The perforated patch method and amperometry were used to determine whether the adrenal medullary cell itself is capable of sensing hypoxia and, if so, how such sensation is transduced to secretion of catecholamines (CA). 2. Exposure to hypoxia, cyanide (CN), or muscarine facilitated CA secretion from dissociated chromaffin cells. The CN-induced secretion was not affected by removal of glucose, indicating that the CN release is due to chemical hypoxia. 3. The secretions induced by CN and muscarine were markedly diminished by removal of Ca2+ ions or by application of Cd2+ or methoxyverapamil (D-600). 4. Cyanide and muscarine produced depolarizations with generation of action potentials and increased intracellular Ca2+ concentrations determined using the acetoxymethyl (AM) ester form of fluo-3 in the presence of external Ca2+ ions, but not in their absence. 5. Hypoxia and CN produced inward currents at an equilibrium potential for Cl- ions, irrespective of whether or not Na+ ions were present in the cells, and substitution of N-methyl-D-glucamine for 134 mM Na+ ions in the perfusate inhibited the CN current by 71 %. The reversal potential for the CN current was -24 mV in the standard perfusate. 6. The hypoxia-, CN- and muscarine-induced currents decreased in parallel with hyperpolarizations, and exposure to CN prevented muscarine, but not nicotine, from inducing a further inward current. 7. We conclude that hypoxia and CN induce CA secretion through depolarization and the subsequent activation of voltage-dependent Ca2+ channels and that this depolarization is due to opening of cation channels, which are possibly identical to muscarinic cation channels.
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