The Double‐ticker: An Improved Fast Drug‐application System Reveals Desensitization of the Glutamate Channel from a Closed State

The present study describes a modification of the fast drug‐application technique (ticker) which combines two fast‐application systems, ‘the double‐ticker’. With the double‐ticker, drugs can be applied to excised patches from either one of the tickers permitting switching among three different solutions in the sub‐millisecond range. We made use of this advantageous feature of the double‐ticker to study two aspects of the glutamate receptor channel in crayfish muscle. The first concerns revealing the number of glutamate binding sites from measurements of a dose‐response relation (2–3 sites). The other relates to the state from which the receptor undergoes desensitization. For the quisqualate‐sensitive glutamate receptor desensitization occurs from a closed state. This is in addition to desensitization from an open state.