Fig. 5.

Ca²⁺ signals in boutons at different external Ca²⁺ levels at 21°C. As [Ca²⁺]_e was increased, a larger Ca²⁺ signal was observed for both controls andcsp^U1 mutants. A,B, Ca²⁺ changes in type Ib boutons of controls (A, n = 12) andcsp^U1 mutants (B,n = 5) with increased [Ca²⁺]_e: 0.5, 1, and 3 mm.Symbols indicate mean ± SEM values at each time point. Preparations were stimulated in HL3 solution at 5 Hz for 5 sec (solid horizontal bar). Large error bars shown at 3 mm [Ca²⁺]_e during stimulation resulted from contraction of the muscle. C, Peak values for intracellular Ca²⁺ signal with different extracellular Ca²⁺ concentrations.