Subcellular Calcium Transients Visualized by Confocal Microscopy in a Voltage-Clamped Vertebrate Neuron

Abstract

Confocal laser-scanned microscopy and long-wavelength calcium (Ca 2+ ) indicators were combined to monitor both sustained and rapidly dissipating Ca 2+ gradients in voltage-clamped sympathetic neurons isolated from the bullfrog. After a brief activation of voltage-dependent Ca 2+ channels, Ca 2+ spreads inwardly, and reaches the center of these spherical cells in about 300 milliseconds. Although the Ca 2+ redistribution in the bulk of the cytosol could be accounted for with a radial diffusion model, local nonlinearities, suggesting either nonuniform Ca 2+ entry or spatial buffering, could be seen. After electrical stimulation, Ca 2+ signals in the nucleus were consistently larger and decayed more slowly than those in the cytosol. A similar behavior was observed when release of intracellular Ca 2+ was induced by caffeine, suggesting that in both cases large responses originate from Ca 2+ release sites near or within the nucleus. These results are consistent with an amplification mechanism involving Ca 2+ -induced Ca 2+ release, which could be relevant to activity-dependent, Ca 2+ -regulated nuclear events.