Direct activation of cloned K(atp) channels by intracellular acidosis.
ATP-sensitive K(+) (K(ATP)) channels may be regulated by protons in addition to ATP, phospholipids, and other nucleotides. Such regulation allows a control of cellular excitability in conditions when pH is low but ATP concentration is normal. However, whether the K(ATP) changes its activity with pH alterations remains uncertain. In this study we showed that the reconstituted K(ATP) was strongly activated during hypercapnia and intracellular acidosis using whole-cell recordings. Further characterizations in excised patches indicated that channel activity increased with a moderate drop in intracellular pH and decreased with strong acidification. The channel activation was produced by a direct action of protons on the Kir6 subunit and relied on a histidine residue that is conserved in all K(ATP). The inhibition appeared to be a result of channel rundown and was not seen in whole-cell recordings. The biphasic response may explain the contradictory pH sensitivity observed in cell-endogenous K(ATP) in excised patches. Site-specific mutations of two residues showed that pH and ATP sensitivities were independent of each other. Thus, these results demonstrate that the proton is a potent activator of the K(ATP). The pH-dependent activation may enable the K(ATP) to control vascular tones, insulin secretion, and neuronal excitability in several pathophysiologic conditions.
Xu
H
H
Department of Biology, Georgia State University, Atlanta, Georgia 30302-4010, USA.
Cui
N
N
Yang
Z
Z
Wu
J
J
Giwa
L R
LR
Abdulkadir
L
L
Sharma
P
P
Jiang
C
C
D018528:ATP-Binding Cassette Transporters; D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000595:Amino Acid Sequence; D000818:Animals; D003001:Cloning, Molecular; D016384:Consensus Sequence; D005260:Female; D006639:Histidine; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D051379:Mice; D008969:Molecular Sequence Data; D009865:Oocytes / Q000187:drug effects / Q000502:physiology*; D015221:Potassium Channels / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D024661:Potassium Channels, Inwardly Rectifying; D021122:Protein Subunits; D011817:Rabbits; D011955:Receptors, Drug / Q000235:genetics / Q000502:physiology*; D011994:Recombinant Proteins / Q000378:metabolism; D016415:Sequence Alignment; D017384:Sequence Deletion; D017386:Sequence Homology, Amino Acid; D064233:Sulfonylurea Receptors; D014982:Xenopus laevis
D018528:ATP-Binding Cassette Transporters; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; D021122:Protein Subunits; D011955:Receptors, Drug; D011994:Recombinant Proteins; D064233:Sulfonylurea Receptors; D006639:Histidine; D000255:Adenosine Triphosphate