Figure 10.

Spontaneous neurotransmitter release in Syb1^lew/lewSyb2^−/− NMJs is insensitive to extracellular Ca²⁺. A, Sample traces of mEPPs recorded in Ringer's solution at increasing extracellular Ca²⁺ concentration ([Ca²⁺]₀, 0, 1, 2, and 4 mM). A continuous recording of 4 min is shown for each cell. Each horizontal line indicates a 1 min continuous recording containing 60 superimposed 1 s traces; 1 mM EGTA was added to 0 mM Ca²⁺ Ringer's solution, and the muscle samples were incubated in this solution for 60 min before recording. B, Quantification of mEPP frequencies. mEPP frequencies correlated with increases in extracellular calcium in control mice but remained insensitive to extracellular calcium in Syb1^lew/lewSyb2^−/− mice. mEPP frequencies (events/min) in controls were as follows: 0 mm Ca²⁺, 0.18 ± 0.06; 1 mM Ca²⁺, 0.57 ± 0.11; 2 mM Ca²⁺, 0.88 ± 0.15; and 4 mM Ca²⁺, 2.05 ± 0.37. mEPP frequencies in Syb1^lew/lewSyb2^−/− mice were as follows: 0 mM Ca²⁺, 4.19 ± 0.49; 1 mM Ca²⁺, 4.46 ± 0.74; 2 mM Ca²⁺, 4.55 ± 0.66; and 4 mM Ca²⁺, 4.47 ± 0.89. Sample sizes: 3 pairs of control and Syb1^lew/lewSyb2^−/− mice were analyzed. Controls, n = 20 cells; Syb1^lew/lewSyb2^−/−, n = 18 cells.