Fig. 4. The [Ca²⁺]_i and force of an OOM during exposure to three concentrations of proctolin. The peptide was applied for 60 s. Time zero is a response before peptide arrival, the other numbers written above the tetani are time in minutes after PR. The tetani were produced by trains of stimuli (1 ms pulses, 30 Hz, 300 ms train duration, 0.1 trains s^-1).