Fig. 3.

Effect of 4-AP on quantal transmitter release in acsp mutant preparation. A ts block of evoked transmitter release was obtained in a csp mutant preparation (as in Fig.1A). 4-AP was added after verifying the block of evoked release at 32°C (note the absence of evoked response at 32°C; − 4AP). No recovery of evoked responses was seen with 4-AP (+ 4AP) at 32°C. However, if one cools the 4-AP-treated preparation to 21°C, one detects the protracted ejp associated with the action of this K channel blocker. Comparable results were obtained in three experiments.