Terbium fluorescence characteristics of cultured neurons using ultraviolet microspectrofluorometry

The fluorescence emission intensity of terbium is enhanced upon the binding of Tb³⁺ to cultured mouse spinal cord and dorsal root ganglion neurons, via nonradiative resonant energy transfer from membrane proteins. The relative fluorescence intensities of Tb³⁺ bound to dorsal root ganglion neurons were considerably greater than that of Tb³⁺ bound to large multipolar spinal cord neurons. The cell bodies of the dorsal root ganglion neurons were completely covered in a dense fluorescent blanket, whereas the fluorescence from the spinal cord soma presented a discontinuous pattern. The neurites of the spinal cord neuron were speckled with bright patches of Tb³⁺ fluorescence. A high concentration of Ca²⁺ reduced the relative fluorescence intensity of the Tb³⁺ -neuron complex. It is suggested that Tb³⁺ binds to Ca²⁺ -binding sites on the surface membrane of neurons.