Subanesthetic doses of ketamine stabilize the fusion pore in a narrow flickering state in astrocytes

Abstract

Ketamine is an anesthetic that exhibits analgesic, psychotomimetic, and rapid antidepressant effects that are of particular neuropharmacological interest. Recent studies revealed astrocytic Ca(2+) signaling and regulated exocytosis as ketamine-targeted processes. Thus high-resolution cell-attached membrane capacitance measurements were performed to examine the influence of ketamine on individual vesicle interactions with the plasma membrane in cultured rat astrocytes. Ketamine evoked long-lasting bursts of repetitive opening and closing of the fusion pore that were both time- and concentration-dependent. Moreover, acute application and subanesthetic doses of ketamine elicited a significant increase in the occurrence of bursts that were characterized by a decreased fusion pore conductance, indicating that the fusion pore was stabilized in a narrow configuration. The time- and concentration-dependent increase in burst occurrence was correlated with a decrease in full fission events. This study has demonstrated a novel effect of ketamine manifested as stabilization of a fusion pore incapable of transiting to full vesicle fission, suggestive of an inhibitory effect on vesicle retrieval. This until now unrecognized effect of ketamine on the vesicle fusion pore might play a role in astroglial release and (re)uptake of molecules, modulating synaptic activity. This study demonstrates a novel effect of ketamine on the fusion pore. High-resolution cell-attached membrane capacitance measurements revealed that ketamine evokes long-lasting flickering of a narrow fusion pore that is incapable of transiting to full fission. Astrocytic vesicle fusion/retrieval modified by subanesthetic ketamine doses most likely affects gliotransmission and indicates a non-neuronal mechanism of ketamine action that may contribute to its behavioral effects.