Sustained hypoxia enhances TASK-like current inhibition by acute hypoxia in rat carotid body type-I cells.
Carotid body type-I cells respond to acute hypoxia with membrane depolarization and calcium-dependent neurotransmitter release. The inhibition of a TASK-like background potassium channels plays a key role in initiating this response. Chronic hypoxia enhances the carotid body chemosensory responses evoked by acute hypoxia, however the accurate mechanism by which chronic hypoxia increases carotid body reactivity is not clear. Therefore, we investigated the effects of chronic hypoxia upon TASK-like currents in isolated type-I cells. Carotid bodies were excised from anaesthetized newborn Sprague-Dawley rats and dissociated by collagenase-trypsin digestion. Isolated cells were maintained under 5% CO(2) in normoxic (21% O(2)) or hypoxic (1-2% O(2)) environment for 24 and 48 hours. Channel activity (NPo) was recorded using the cell-attached configuration of the patch-clamp technique. In normoxic and 24 hours hypoxic cultured cells, acute hypoxic stimuli decreases NPo approximately 70% with no effects on current amplitude. On the other hand, in cultured cells subjected to 48 hours of hypoxia, NPo decreases near to 90% in response to acute hypoxia. We concluded that continuous hypoxic exposure enhances the TASK-like channel activity inhibition in response to acute hypoxia. Our results provide a potential mechanism by which chronic hypoxia increases carotid body reactivity.
Ortiz
F
F
Laboratory of Neurobiology, Faculty of Biological Sciences, Pontificia Universidad Católica de Chile, Casilla 114-D, Portugal 49, Santiago, Chile. induchuna@yahoo.es
Iturriaga
R
R
Varas
R
R
D000818:Animals; D002344:Carotid Body / Q000166:cytology* / Q000378:metabolism*; D004553:Electric Conductivity; D000860:Hypoxia / Q000378:metabolism*; D008297:Male; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013997:Time Factors
D015221:Potassium Channels