ABSTRACT
Application of ketamine (10−4–10−3mol l−1) to locust retractor unguis muscle produced a reversible, dose-dependent reduction in neurally evoked twitches, and blocked agonist-induced contractions. With increasing ketamine concentration (5×10−5–10−3mol l−1), the amplitude of glutamate potentials was reduced and dose-response curves for ionophoresis of L-glutamate were shifted to the right, particularly after concanavalin A treatment. Ketamine (10−4mol l−1) enhanced the rate of desensitization to consecutive pulses of L-glutamate and this action was eliminated by concanavalin A. The amplitude of the excitatory postsynaptic current (EPSC) was reduced by ketamine (10−5×5×10−4mol l−1) in a dosedependent manner but without a concomitant reduction in EPSC rise time. The decay phase of the EPSC was usually biphasic in the presence of ketamine (>5×10−5mol l−1) but did not exhibit any voltage dependence. It is concluded that ketamine enhances desensitization and blocks the channel, particularly the closed form.
