CONNEXIN37 FORMS HIGH-CONDUCTANCE GAP JUNCTION CHANNELS WITH SUBCONDUCTANCE STATE ACTIVITY AND SELECTIVE DYE AND IONIC PERMEABILITIES

Gap junctions are thought to mediate the direct intercellular coupling of adjacent cells by the open-closed gating of an aqueous pore permea ble to ions and molecules of up to 1 kDa or 10-14 Angstrom in diameter . We symmetrically altered the ionic composition or asymmetrically add ed 6-carboxyfluorescein (6-CF, M(r) = 376), a fluorescent tracer, to p airs of connexin37-transfected mouse neuro2A cells to examine the ioni c and dye permeability of human connexin37 channels. We demonstrate th at the 300-pS channel formed by connexin37 has an effective relative a nion/cation permeability ratio of 0.43, directly converts to at least one intermediate (63 pS) subconductance state, and that 6-CF dye trans fer is accompanied by a 24% decrease in unitary channel conductance. T hese observations favor a new interpretation of the gap junction pore consistent with direct ion-channel interactions or electrostatic charg e effects common to more conventional multistate ion channels. These r esults have distinct implications about the different forms of interce llular signaling (cationic, ionic, and/or biochemical) that can occur depending on the expression and conformation of the connexin channel p roteins.