Functinal regulation of cardiac ATP-sensitive potassium channel by actin cytoekeleton

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Previously, we had reported that ATP-sensitive potassium channel (K_<ATP> channel)^- required intracellular ATP to maintain its activity and that this effect of ATP is similar to ATP action on polymerization/depolymerization of actin cytoskeleton. Thus, we examined functional modulation of K_<ATP> channel by cytoskeleton.Actin disruptors diminished K_<ATP> channel activity, while actin stabilizer maintained channel activity. Disruptors or stabilizers of microtubules did not affect K_<ATP> channel activity. Direct application of polymerized form of actin (F-actin) recovered lost channel activity. PIP_2, which binds to all actin binding proteins and inhibits their actin severing activity, act for maintainance of channel activity and recevered prtially lost channel activity. These data indicate that K_<ATP> channel activity was functionally modulated by the status of actin cytoskeleton.Next, we sought using yeast two hybrid system protein that would interact with nucleotide binding domain (NBD) of sulfonylurea receptor (SUR), a target of intracellular regulation of K_<ATP> channel. An unknown protein was found to interact with NBD1 of cardiac type SUR,(SUR2a), whose transcript are present ubiquitously and most predominantly in the heart. Isolation of full-length of cDNA revealed that there were four isoforms due to alternative splicing. In each isoform, there was a region that had high sequence homology to cytochrome C.Thus, K_<ATP> channel might be regulated by intracellular oxidization reaction.Currently, we are on the way to examine functional role of interaction of NBD1 in SUR2a and the unknown protein that we found.