Activation of an ATP-dependent K(+) conductance in Xenopus oocytes by expression of adenylate kinase cloned from renal proximal tubules.
In rabbit proximal convoluted tubules, an ATP-sensitive K(+) (K(ATP)) channel has been shown to be involved in membrane cross-talk, i.e. the coupling (most likely mediated through intracellular ATP) between transepithelial Na(+) transport and basolateral K(+) conductance. This K(+) conductance is inhibited by taurine. We sought to isolate this K(+) channel by expression cloning in Xenopus oocytes. Injection of renal cortex mRNA into oocytes induced a K(+) conductance, largely inhibited by extracellular Ba(2+) and intracellular taurine. Using this functional test, we isolated from our proximal tubule cDNA library a unique clone, which induced a large K(+) current which was Ba(2+)-, taurine- and glibenclamide-sensitive. Surprisingly, this clone is not a K(+) channel but an adenylate kinase protein (AK3), known to convert NTP+AMP into NDP+ADP (N could be G, I or A). AK3 expression resulted in a large ATP decrease and activation of the whole-cell currents including a previously unknown, endogenous K(+) current. To verify whether ATP decrease was responsible for the current activation, we demonstrated that inhibition of glycolysis greatly reduces oocyte ATP levels and increases an inwardly rectifying K(+) current. The possible involvement of AK in the K(ATP) channel's regulation provides a means of explaining their observed activity in cytosolic environments characterized by high ATP concentrations.
Brochiero
E
E
Département de Physiologie, Université de Montréal, Quebec, Canada. brochiee@magellan.umontreal.ca
Coady
M J
MJ
Klein
H
H
Laprade
R
R
Lapointe
J Y
JY
D000255:Adenosine Triphosphate / Q000032:analysis; D000263:Adenylate Kinase / Q000096:biosynthesis* / Q000737:chemistry / Q000235:genetics; D000595:Amino Acid Sequence; D000818:Animals; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000096:biosynthesis / Q000737:chemistry; D004563:Electrochemistry; D015723:Gene Library; D005905:Glyburide; D066298:In Vitro Techniques; D007687:Kidney Tubules, Proximal / Q000378:metabolism*; D008353:Mannitol; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D009865:Oocytes / Q000187:drug effects / Q000378:metabolism*; D015221:Potassium Channels / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D012333:RNA, Messenger / Q000032:analysis / Q000378:metabolism; D011817:Rabbits; D016415:Sequence Alignment; D013654:Taurine; D014162:Transfection; D014981:Xenopus
D018076:DNA, Complementary; D008565:Membrane Proteins; D015221:Potassium Channels; D012333:RNA, Messenger; C117780:mitochondrial K(ATP) channel; D013654:Taurine; D008353:Mannitol; D000255:Adenosine Triphosphate; D000263:Adenylate Kinase; D005905:Glyburide