Fig. 2.

Spontaneous firing is Na⁺ dependent and not blocked by streptomycin. A: spontaneous action potentials recorded in current clamp in a CZ calyx terminal. A current injection (−100 pA, 20-ms duration) at the start of each recording elicited a hyperpolarizing voltage deflection (arrow) that served to monitor stability of the recording over time. Action potentials were abolished when choline chloride replaced NaCl in the external HEPES solution bathing the slice (center) and returned after a wash (right). B: action potentials recorded from a PZ calyx terminal persisted after extracellular application of 0.5 mM streptomycin sulfate.