Figure 4.

The transient block of Ca²⁺ current requires the exocytosis of synaptic vesicles. A, Diagram showing that H⁺ (gray) ions are released from fused vesicles during exocytosis and can affect adjacent Ca²⁺ channels at an active zone of release (blue). B, After the dialysis of 10 mm BAPTA into a hair cell, Ca²⁺ currents were evoked by a 500 ms pulse from −90 mV (black) or from −60 mV (red) to −30 mV. Note that Ca²⁺ currents do not show the transient block now that exocytosis has been severely decreased by 10 mm BAPTA. C, 10 mm methylamine was added to the internal pipette solution. This removed the transient block, which went from 81 ± 15 to 0 pA (n = 6, p = 0.0028, paired t test) without significant changes in ΔC_m (136 ± 2.4 fF in control and 126 ± 4.8 fF in 10 mm methylamine, n = 6, p > 0.05, paired t test). The Ca²⁺ current was evoked by a 500-ms-long pulse from a holding potential of −60 to −30 mV. The Ca²⁺ currents were recorded in control (black) with a first patch pipette and then, after repatching the same hair cell, using a second pipette containing 10 mm methylamine (red).