Am J Physiol Cell Physiol AJP: Cell Physiology
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Am J Physiol Cell Physiol (October 22, 2003). doi:10.1152/ajpcell.00401.2003
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Submitted on September 22, 2003
Accepted on October 16, 2003

System-specific O2-sensitivity of the tandem-pore-domain K+ channel TASK-1

Rosalyn P Johnson1, Ita M O'Kelly1, and Ian M Fearon1*

1 Department of Biology, McMaster University, Hamilton, ON, Canada

* To whom correspondence should be addressed. E-mail: fearoni{at}mcmaster.ca.

Hypoxic inhibition of TASK-1 (Kcnk3 or K2P3.1), a tandem-pore-domain background K+ channel, provides a critical link between reduced O2 levels and physiological responses in various cell types. Here, we examined the expression and O2-sensitivity of TASK-1 in immortalised adrenomedullary chromaffin (MAH) cells. In physiological (asymmetrical) K+ solutions, 3 µM anandamide or 300 µM Zn2+ inhibited a strongly pH-sensitive current. Under symmetrical K+ conditions, the anandamide and Zn2+-sensitive K+ currents were voltage-independent. These data demonstrate the functional expression of TASK-1, and cellular expression of this channel was confirmed by RT-PCR and Western blotting. At concentrations which selectively inhibit TASK-1, anandamide and Zn2+ were without effect on the magnitude of the O2-sensitive current or the hypoxic depolarisation. Thus, TASK-1 does not contribute to O2 sensing in MAH cells, and demonstrates the failure of a known O2-sensitive K+ channel to respond to hypoxia in an O2-sensing cell type. These data demonstrate that ultimately the sensitivity of a particular K+ channel to hypoxia is determined by the cell, and we propose this is achieved by coupling distinct hypoxia signalling systems to individual channels. Importantly, these data also reiterate the indirect O2-sensitivity of TASK-1, which appears to require the presence of an intracellular mediator.




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