Figure 8.

Ca²⁺-dependent axon terminal excitability. A. Spontaneous (●) and electrotonically evoked (△) long-lasting plateau ejps recorded intracellularly in the presence of Na⁺ and K⁺ channel blockers (3 µM TTX, 200 µM 4-AP, 20 µM TEA, and 100 µM quinidine in HL3.1 saline containing 0.1 mM Ca²⁺, see Methods). Evoked plteau ejps are also displayed with a faster time scale in lower traces. Plateau ejps, observed only after inhibiting K⁺ channel function, reflect transmitter release caused by prolonged presynaptic depolarization (see text). Occurrence of both spontaneous and evoked plateau ejps was decreased in rut. These plateau ejps were suppressed by the Ca²⁺ channel blocker Co²⁺ (60 µM). B. Reduced probability of evoking plateau ejps by electrotonic stimulation in rut¹. C. Reduced frequency of spontaneously occurring plateau ejps in two rut alleles. Spontaneous plateau ejps varied in amplitude and only those with amplitude ≥ 20 % of maximally attainable plateau ejps in the same branch were included in the samples. *, p < 0.05; t-test. Mean and SEM from the number of terminals examined are indicated.