Transporter Current Measurements

Na⁺ /K⁺ pump, Na⁺ /Ca²⁺ exchanger, glutamate transporter and other transporters for dopamine, norepinephrine, GABA, and others, are all electrogenic. These transporters or exchanger transport Na⁺ ions, with or without transmitters, in or out of the cells, while K₊ or Ca²⁺ , sometimes with anions, are transported to the opposite direction. Since more Na⁺ is transported, it induces net positive charge movement, therefore producing membrane currents in the direction of Na⁺ ion movement. Na⁺ /K⁺ pump can work against ion gradient because it is an ATPase (Na⁺ /K⁺ -ATPase). In addition, under a certain condition, the Na⁺ /K⁺ pump transforms into an ion channel so that it produces pump-channel currents. Other exchangers and transporters are generally dependent on electrochemical potential gradients and also voltage-dependent.