Na+ pump inhibition and non-selective cation channel activation by cyanide and anoxia in guinea-pig chromaffin cells.
1. Hypoxia and metabolic inhibition with cyanide (CN) evoke catecholamine secretion in adrenal chromaffin cells through depolarization. We elucidated mechanisms for a CN- or anoxia-induced inward (depolarization) current, using the perforated patch method. 2. Bath application of Ba2+ induced a dose-dependent inhibition of a muscarine-induced current (IMUS) and part of the CN-induced current (ICN) with an IC50 (concentration responsible for 50 % inhibition) of 1.3 mM. The Ba2+-sensitive component was estimated to comprise 58 % of the total ICN. 3. The Ba2+-resistant component of ICN tended to increase with shifts of membrane potential from -40 to 40 mV and was markedly suppressed by exposure to a K+-free solution or 200 microM ouabain, indicating that the majority of the Ba2+-resistant component of ICN is due to suppression of the Na+ pump current (Ipump). 4. The non-Ipump component of ICN diminished progressively in K+-free solution. Substitution of glucose for sucrose in a K+-free CN solution further diminished the CN potency to produce the non-Ipump component. 5. The I-V relationship for the non-Ipump component of ICN had a reversal potential of -3 and -47 mV at 147 and 5.5 mM Na+, respectively, and showed an outward rectification, indicating that the non-Ipump component of ICN is due to activation of non-selective cation channels. 6. Exposure to anoxia induced a current with an amplitude comparable to that of ICN, and the anoxia-induced current apparently occluded development of ICN. The anoxia-induced current diminished by ca 60 % in the absence of K+ and reversed polarity at 5 mV under K+-free conditions. 7. It is concluded that exposure to CN and to anoxia induces suppression of the Na+ pump and activation of non-selective cation channels, probably due to an ATP decrease resulting mainly from consumption by the Na+ pump.
Inoue
M
M
Department of Physiology, School of Medicine, Fukuoka University, Fukuoka 814 0180, Japan. minoue@fukuoka-u.ac.jp
Fujishiro
N
N
Imanaga
I
I
D000818:Animals; D001464:Barium / Q000494:pharmacology; D002412:Cations / Q000378:metabolism; D015687:Cell Hypoxia / Q000187:drug effects / Q000502:physiology*; D019439:Chromaffin Cells / Q000187:drug effects / Q000378:metabolism*; D003486:Cyanides / Q000494:pharmacology*; D004594:Electrophysiology; D005260:Female; D006168:Guinea Pigs; D066298:In Vitro Techniques; D007473:Ion Channels / Q000819:agonists*; D009116:Muscarine / Q000494:pharmacology; D018721:Muscarinic Agonists / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D011976:Receptors, Muscarinic / Q000187:drug effects / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors*
D002412:Cations; D003486:Cyanides; D007473:Ion Channels; D018721:Muscarinic Agonists; D011976:Receptors, Muscarinic; D001464:Barium; D009116:Muscarine; D000254:Sodium-Potassium-Exchanging ATPase