Molecular regions responsible for differences in activation between heag channels.

The ether-a-go-go potassium channels heag1 and heag2 are highly homologous; however, the activation properties between the two channels are different. We have studied the molecular regions that determine differences in activation properties by making chimeras between the two channels, expressing them in oocytes, and recording currents with two-electrode voltage-clamp. The activation time course has an initial sigmoidal component dependent on the Cole-Moore shift, followed by a faster component. We show that not only is the extreme N terminus involved in differences between heag1 and heag2 channels, but also the PAS domain itself. Also multiple regions of the membrane-spanning part of the channel appear to be involved, with different regions involved for the early and late time courses, reflecting their different mechanisms. The later time course involved S1 and P-S6 regions. Taken together, our data show that activation involves multiple regions of the N terminal region and membrane-spanning regions of the channel.