| Research Abstract |
ATP-sensitive K^+ (K_<ATP>) channels open and close depending on ATP concentration in the cytoplasm, and control excitability of the cells. We have previously shown that K_<ATP> channel of pancreatic β-cell comprises SUR1, a member of ABC protein, and Kir6.2, a member of inward rectifier K channels. In heart and skeletal muscles, and blood vessels, K_<ATP> channels of similar properties comprise SUR2A/B and Kir6.x, regulating muscle contraction during hypoxia or ischemia.
Although similar K_<ATP> channel is expressed in mitochondria, and regulating energy metabolism, its constituting molecules are unknown.
Using the patch-clamp technique, we recorded ion channel activity from the mitochondrial inner membrane of Jurkat cells. K^+ ion selective channels with conductance of 55 pS were observed, of which activity being suppressed by 2 mM ATP.These properties and burst kinetics are similar to the channel comprising Kir6.1 molecule. In other to study if Kir6.1 molecules are induced during hypo
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xia, A7r5 cells, derived from blood vessel were cultured in medium containing Co^<2+> ions, mimicking hypoxic conditions. Western blotting using anti Kir6.1 antibody revealed that Kir6.1 protein became expressed in 3-4 days after an addition of the ions. However, no activity of channels comprising activity Kir6.1 was observed in the plasma membrane of heart of blood vessel muscles. Following these results, a possibility that Kir6.1 molecule induced in ischemia composes mitochondrial K_<ATP> channel is currently investigated.
In other series of experiments effects of protein kinase A mediated phosphorylation of K_<ATP> channels comprising SUR1 and Kir6.2 were studied. We found both subunits are phosphorylated and channel properties are modulated in a different manner.
Finally, effects of anti-diabetic reagents, troglitazone, pioglitazone, and KAD-1229, were studied on reconstituted K_<ATP> channels. The studies are helpful in understanding structure-function relationship of K_<ATP> channels in the plasma membrane as well as mitochondria. Less
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