Purinergic signalling - a possible mechanism for KCNQ1 channel response to cell volume challenges.
OBJECTIVE
A number of K(+) channels are regulated by small, fast changes in cell volume. The mechanisms underlying cell volume sensitivity are not known, but one possible mechanism could be purinergic signalling. Volume activated ATP release could trigger signalling pathways that subsequently lead to ion channel stimulation and cell volume back-regulation. Our aim was to investigate whether volume sensitivity of the voltage-gated K(+) channel, KCNQ1, is dependent on ATP release and regulation by purinergic signalling.


METHODS
We used Xenopus oocytes heterologously expressing human KCNQ1, KCNE1, water channels (AQP1) and P2Y2 receptors. ATP release was monitored by a luciferin-luciferase assay and ion channel conductance was recorded by two-electrode voltage clamp.


RESULTS
The luminescence assay showed that oocytes released ATP in response to mechanical, hypoosmotic stimuli and hyperosmotic stimuli. Basal ATP release was approx. three times higher in the KCNQ1 + AQP1 and KCNQ1 injected oocytes compared to the non-injected ones. Exogenously added ATP (0.1 mm) did not have any substantial effect on volume-induced KCNQ1 currents. Nevertheless, apyrase decreased all currents by about 50%. Suramin inhibited about 23% of the KCNQ1 volume sensitivity. Expression of P2Y2 receptors stimulated endogenous Cl(-) channels, but it also led to 68% inhibition of the KCNQ1 currents. Adenosine (0.1 mm) also inhibited the KCNQ1 currents by about 56%.


CONCLUSIONS
Xenopus oocytes release ATP in response to mechanical stimuli and cell volume changes. Purinergic P2 and P1 receptors confer some of the KCNQ1 channel volume sensitivity, although endogenous adenosine receptors and expressed P2Y2 receptors do so in the negative direction.
Department of Biology, University of Copenhagen, Copenhagen, Denmark.
S
S
Hammami
N J
NJ
Willumsen
A-K
AK
Meinild
D A
DA
Klaerke
I
I
Novak
D000241:Adenosine / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D051398:Aquaporin 1 / Q000235:genetics / Q000378:metabolism; D048429:Cell Size / Q000187:drug effects; D017930:Genes, Reporter; D006801:Humans; D015640:Ion Channel Gating; D051657:KCNQ1 Potassium Channel / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D040542:Mechanotransduction, Cellular / Q000187:drug effects; D008564:Membrane Potentials; D009865:Oocytes / Q000378:metabolism*; D009997:Osmotic Pressure; D018408:Patch-Clamp Techniques; D024642:Potassium Channels, Voltage-Gated / Q000235:genetics / Q000378:metabolism; D058914:Purinergic Antagonists / Q000494:pharmacology; D011983:Receptors, Purinergic / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D058473:Receptors, Purinergic P2Y2 / Q000378:metabolism; D014982:Xenopus laevis
C496020:AQP1 protein, human; C489622:KCNE1 protein, human; D051657:KCNQ1 Potassium Channel; C496909:KCNQ1 protein, human; D024642:Potassium Channels, Voltage-Gated; D058914:Purinergic Antagonists; D011983:Receptors, Purinergic; D058473:Receptors, Purinergic P2Y2; D051398:Aquaporin 1; D000255:Adenosine Triphosphate; D000241:Adenosine