Changes in the kinetics and conductance of N-methyl-D-aspartate (NMDA)-receptor activated single channels with temperature.

Single channel currents activated by N-methyl-D-aspartate (NMDA) were recorded in inside-out membrane patches from hippocampal pyramidal cells. The effects of temperature on the conductance level and the kinetics of single channels were accurately determined by using a digital signal processing technique based on hidden Markov models. With increasing temperature, the probability of the channel being in the open state increases steeply, as does the amplitude of channel currents. The proportional change in channel conductance with increasing temperature is greater than the corresponding change in bulk conductivity of 150 mM electrolyte solutions. From the temperature dependence of channel conductance and kinetics, we derived several thermodynamical properties of the NMDA-receptor activated channel. Among these are the height of the energy barrier V presented to an ion traversing the pore, the activation energy Ea and the enthalpy delta H of the channel.