KETAMINE BLOCKS CURRENTS THROUGH MAMMALIAN NICOTINIC ACETYLCHOLINE-RECEPTOR CHANNELS BY INTERACTION WITH BOTH THE OPEN AND THE CLOSED STATE

Single channel recordings have shown that ketamine (Ket) decreases the open time of the nicotinic acetylcholine receptor channel (nAChR). Th e present experiments on simultaneous openings of the nAChRs of mouse myotubes investigate the interaction of Ket with the open as well as w ith the closed state of the channels. The patch-clamp technique was us ed to record currents activated by 10(-4) M acetylcholine (ACh) in the outside-out mode. ACh together with increasing concentrations of Ket was applied with a piezo-driven system. In a second protocol, the patc hes were preexposed to Ket before activation with ACh. With addition o f Ket, the currents showed a biexponential decay, indicating an open-c hannel block. The peak current amplitude decreased reversibly and in a concentration-dependent manner. The rate constants of block (b(+1)) a nd of unblock (b(-1)) were modeled by computer simulation and were fou nd to be: b(+1) = 3 x 10(6) M/s, b(-1) = 100/s. Preexposure of the pat ches to Ket revealed an additional block with a K-D of approximately 2 x 10(-6) M, which is below clinical concentrations. These data sugges t that Ket also interacts with the closed state of the nAChR.