Fig. 5.

Action of ionomycin on a csp mutant preparation. In the top (21°C), mejps (first two traces) and the ejp are shown in acsp mutant preparation at permissive temperature. The characteristic failure of the ejp, but not the mejps, is illustrated in the center (32°C). Finally, the effect of ionomycin to increase dramatically the frequency of mejps is shown in the bottom (29°C). At this time, the evoked response remains inhibited (final record), indicating that ionomycin promotes quantal secretion (mejps) at a time when evoked responses (ejps) are blocked. This result is representative of data obtained in three separate experiments.