Table 1.

Abundance of calcium spots, ribbons, and dense bodies in bipolar and hair cells

	Density (μm−2)	SE	Cells
Bipolar cells
Calcium spots	0.11	0.02	17
Ribbons (bottom surface)	0.10	0.01	30
Ribbons (top surface)	0.09	0.01	30
Active zones	0.10	0.03	7
Total fusion sites	0.24	0.04	7
Hair cells
Calcium spots	0.034	0.008	7
Dense bodies	0.048	0.008	8

Ca spots were counted from images as in Figures 1D and8D. CtBP-positive spots were counted from images that summed the bottom-most two images in stacks of serial confocal sections as in Figures 5C and 9B; the spots were considered to represent single ribbons in bipolar cells and dense bodies in hair cells. For bipolar cells, this table also shows the number of active zones of exocytosis (Zenisek et al., 2000) and the total number of fusion sites as determined in Figure 6. Data refer to the bottom surface of cells in which they adhere to the glass coverslip, except that CtBP-positive spots were counted in bipolar cells also on the top surface of the cell.