NMDA receptors

Electrophysiological properties of an NMDA receptor channel in the absence of extracellular Mg²⁺ ions. (a) Outside-out patch clamp recordings of an NMDA (10 micromol/l) activates channel. At -60 mV NMDA evokes an inward unitary current i_N (downward deflection), and at +40 mV the evoked current is outward (upward deflection). (b) i_N/V relation obtained from the averages of unitary currents i_N recorded from a homogeneous population of channels (a population that shows a 40-50 pS unitary conductance). This curve is described by the linear equation i_N = gamma_N (V_m - E_rev) (between -80 mV and +60 mV) and shows that the unitary conductance of NMDA channels is only slightly voltage dependent in the absence of Mg²⁺ ions. Composition of the solutions: intrapipette or intracellular solution (in mmol/l): 140 CsCl, 5K-EGTA and 0.5 CaCl₂; extracellular solution: 140 NaCl, 2.8 KCl and 1 CaCl₂.