Figure 12.

Spontaneous transmitter release in Syb1^lew/lewSyb2^−/− NMJs persists despite the withdrawal of both extracellular and intracellular Ca²⁺. A, B, Sample traces of mEPPs recorded in normal Ringer's solution (2 mm Ca²⁺) (A), and in Ca²⁺-free Ringer's solution containing EGTA (1 mM) and BAPTA-AM (10 μm) (B). Each horizontal line indicates 30 superimposed 1 s traces. A 3 min continuous recording is shown for each cell. C, Bar graphs illustrating mEPP frequencies (events/min) recorded in normal Ringer's solution (open bar) and those in Ca²⁺-free Ringer's (gray bar) in control, Syb1^lew/lew, Syb2^−/−, and Syb1^lew/lewSyb2^−/− mice. mEPP frequencies were significantly (***) reduced in control (p = 8.45 × 10⁻⁷), Syb1^lew/lew (p = 5.15 × 10⁻⁹), and Syb2^−/− (p = 3.47 × 10⁻⁹) when normal Ringer's solution was replaced with Ca²⁺-free Ringer's solution. In contrast, no significant difference (p = 0.91) was found in mEPP frequencies in Syb1^lew/lewSyb2^−/− mice recorded in normal Ringer's solution versus Ca²⁺-free Ringer's solution. D, Sample EPP traces recorded in normal and calcium-free Ringer's solutions. EPPs were completely abolished in control, Syb1^lew/lew, Syb2^−/−, and Syb1^lew/lewSyb2^−/− muscles when recorded in calcium-free Ringer's solution (black arrowheads point to stimulus artifact). Controls, n = 28 cells, N = 4 mice; Syb1^lew/lew, n = 25 cells, N = 3 mice; Syb2^−/−, n = 37 cells, N = 5 mice; and Syb1^lew/lewSyb2^−/−, n = 34 cells, N = 4 mice. n.s., no significant difference (p = 0.91).