RECONSTITUTION OF A K-ATP CHANNEL FROM BASOLATERAL MEMBRANES OF NECTURUS ENTEROCYTES

We have previously reported that basolateral membrane vesicles isolate d from Necturus maculosa small intestinal epithelial cells and incorpo rated into planar phospholipid bilayers display a highly selective ''m axi''-conductance K+ channel whose open-time probability is affected b y voltage. We now report that this channel is inhibited by MgATP in th e solution bathing the intracellular face of the channel but not by Mg 2+ or the Na+ or K+ salts of ATP; the effects of MgATP can be prevente d or reversed by MgADP. The channel is also inhibited by the nonhydrol yzable ATP analogue magnesium adenosine 5'-O-(3-thiotriphosphate) and the sulfonylurea derivatives tolbutamide and glibenclamide; all of the se agents are effective in the intracellular compartment but not when added to the extracellular compartment alone. Channel activity is stim ulated by the ''K+ channel opener,'' diazoxide, which also reverses th e effect of glibenclamide but not of MgATP. The possible role of this channel as a mediator of the parallelism between basolateral membrane Na+-K+ pump activity and the macroscopic K+ conductance of that barrie r is discussed.