Characterization of an ATP-sensitive K+ channel in rat carotid body glomus cells

Carotid body glomus (CB) cells express different types of K+ channels such as TASK, BK, and Kv channels, and hypoxia has been shown to inhibit these channels. Here we report the presence of a ∼72-pS channel that has not been described previously in CB cells. In cell-attached patches with 150 mM K+ in the pipette and bath solutions, TASK-like channels were present (∼15 and ∼36-pS). After formation of inside-out patches, a 72-pS channel became transiently active in ∼18% of patches. The 72-pS channel was K+-selective, inhibited by 2–4 mM ATP and 10–100 μM glybenclamide. The 72-pS channel was observed in CB cells isolated from newborn, 2–3 week and 10–12 week-old rats. Reverse transcriptase-PCR and immunocytochemistry showed that Kir6.1, Kir6.2, SUR1 and SUR2 were expressed in CB glomus cells as well as in non-glomus cells. Acute hypoxia (∼15 mmHg O2) inhibited TASK-like channels but failed to activate the 72-pS channel in cell-attached CB cells. K+ channel openers (diazoxide, pinacidil, levcromakalim), sodium cyanide and removal of extracellular glucose also did not activate the 72-pS channel in the cell-attached state. The hypoxia-induced elevation of intracellular [Ca2+] was unchanged by glybenclamide or diazoxide. NaCN-induced increase in [Ca2+] was not affected by 10 μM glybenclamide but inhibited by 100 μM glybenclamide. Acute glucose deprivation did not elevate [Ca2+] in the presence or absence of glybenclamide. These results show that an ATP-sensitive K+ channel is expressed in the plasma membrane of CB cells, but is not activated by short-term metabolic inhibition. The functional relevance of the 72-pS channel remains to be determined.