Norepinephrine transporters have channel modes of conduction.
Neurotransmitter transporters couple to existing ion gradients to achieve reuptake of transmitter into presynaptic terminals. For coupled cotransport, substrates and ions cross the membrane in fixed stoichiometry. This is in contrast to ion channels, which carry an arbitrary number of ions depending on the channel open time. Members of the gamma-aminobutyric acid transporter gene family presumably function with fixed stoichiometry in which a set number of ions cotransport with one transmitter molecule. Here we report channel-like events from a presumably fixed stoichiometry [norepinephrine (NE)+, Na+, and Cl-], human NE (hNET) in the gamma-aminobutyric acid transporter gene family. These events are stimulated by NE and by guanethidine, an hNET substrate, and they are blocked by cocaine and the antidepressant desipramine. Voltage-clamp data combined with NE uptake data from these same cells indicate that hNETs have two functional modes of conduction: a classical transporter mode (T-mode) and a novel channel mode (C-mode). Both T-mode and C-mode are gated by the same substrates and antagonized by the same blockers. T-mode is putatively electrogenic because the transmitter and cotransported ions sum to one net charge. However, C-mode carries virtually all of the transmitter-induced current, even though it occurs with low probability. This is because each C-mode opening transports hundreds of charges per event. The existence of a channel mode of conduction in a previously established fixed-stoichiometry transporter suggests the appearance of an aqueous pore through the transporter protein during the transport cycle and may have significance for transporter regulation.
T10 T11 T12 T13 T14 T15 T16 T17 T18 T19 T1 T20 T21 T2 T3 T4 T5 T6 T7 T8 T9
CHEMICAL CHEMICAL CHEMICAL CHEMICAL GENE-N GENE-N GENE-N GENE-Y GENE-N GENE-Y CHEMICAL GENE-Y GENE-Y CHEMICAL CHEMICAL CHEMICAL CHEMICAL CHEMICAL CHEMICAL CHEMICAL CHEMICAL
cocaine desipramine NE Norepinephrine Neurotransmitter transporters ion channels gamma-aminobutyric acid transporter hNET gamma-aminobutyric acid transporter hNET gamma-aminobutyric acid hNETs Norepinephrine transporters norepinephrine NE Na+ Cl- NE gamma-aminobutyric acid NE guanethidine