Depolarization increases the single-channel conductance and the open probability of crayfish glutamate channels.
We have studied the voltage sensitivity of glutamate receptors in outside-out patches taken from crayfish muscles. We found that single-channel conductance, measured directly at the single-channel level, increases as depolarization rises. At holding potentials from -90 mV to approximately 20 mV, the conductance is 109 pS. At holding potentials positive to 20 mV, the conductance is 213 pS. This increase in single-channel conductance was also observed in cell-attached patches. In addition, desensitization, rise time, and the dose-response curve were all affected by depolarization. To further clarify these multifaceted effects, we evaluated the kinetic properties of single-channel activity recorded from cell-attached patches in hyperpolarization (membrane potential around -75 mV) and depolarization (membrane potential approximately 105 mV). We found that the glutamate dissociation rate constant (k_) was affected most significantly by membrane potential; it declined 6.5-fold under depolarization. The rate constant of channel closing (k(c)) was also significantly affected; it declined 1.8-fold. The rate constant of channel opening (k(o)) declined only 1.2-fold. The possible physiological significance of the depolarization-mediated changes in the above rate constants is discussed.
Tour
O
O
Otto Loewi Center for Cellular and Molecular Neurobiology, and Department of Neurobiology, The Hebrew University, Jerusalem, Israel. tour@vms.huji.ac.il
Parnas
H
H
Parnas
I
I
D000818:Animals; D003400:Astacoidea / Q000378:metabolism*; D055592:Biophysical Phenomena; D001703:Biophysics; D004305:Dose-Response Relationship, Drug; D004553:Electric Conductivity; D018698:Glutamic Acid / Q000008:administration & dosage; D007473:Ion Channels / Q000187:drug effects / Q000378:metabolism*; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects; D009132:Muscles / Q000187:drug effects / Q000378:metabolism; D018408:Patch-Clamp Techniques; D017470:Receptors, Glutamate / Q000187:drug effects / Q000378:metabolism*
D007473:Ion Channels; D017470:Receptors, Glutamate; D018698:Glutamic Acid