Transmitter release during repetitive stimulation: selective changes produced by Sr2+ and Ba2+.

The addition of Sr2+ or Ba2+ to the solution bathing the frog neuromuscular junction leads to an increased release of transmitter by each nerve impulse during and following repetitive stimulation. The mechanisms by which Sr2+ and Ba2+ increase release are not the same. Each ion appears to act selectively on a different process involved in transmitter release.