COMPARATIVE ASPECTS OF IONIC CONDUCTANCES IN NERVE AND HEART CELL MEMBRANES

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This project is concerned with a comparative analysis of ion channels in nerve and heart cell membranes and the relationship of these channels to excitability in both preparations. During the past year, one of the primary experimental preparations has been the axoplasm from squid giant axons. The axoplasm has been previously shown to contain organelles which, in turn, contain potassium and sodium ion channels that are virtually identical to the respective ion channels underlying excitability in the axolemma. Those organelles appear to fuse with the axonal membrane, thereby replenishing these channels in the axon. This project has focused on a follow-up to these original observations. One major finding has been that the organelles can be separated on the basis of size using control-pore-size, glass bead chromatography. One major organelle fraction obtained with this chromatography technique lies near the 50 nm size point of the glass bead column, which probably corresponds to anterograde organelles. These organelles were also found to contain sodium and potassium ion channels based on recordings of electric currents from channels incorporated in artificial lipid bilayers.