Ca～(2+) Sparks And Ca～(2+) Glows In Superior Ganglion Neurons

As a ubiquitous intracellular messenger, Ca²⁺ plays critical roles in a myriad of physiological processes, including muscle contraction, synaptic transmission, hormone secretion, gene transcription, cell survival, and cell death. Ca release from the endoplasmic reticulum (ER) is an integral component of neuronal Ca signaling. The present study is to investigate properties of local Ca²⁺ release events in superior cervical ganglion (SCG) neurons.Primary cultured SCG neurons were prepared from neonatal rats (P3^P7). Low concentration of caffeine was used to induce Ca²⁺ release from the ER Ca²⁺ store, and intracellular Ca²⁺ was recorded by high-resolution line scan confocal imaging and the Ca²⁺ indicator fluo-4. We found two populations of local Ca²⁺ release events with distinct temporal characteristics were evoked by 1.5 mM caffeine near the surfacemembrane in the soma and the neurites of SCG neurons. Brief events similar to classic Ca sparks lasted a few hundreds of milliseconds, whereas long-lasting events displayed duration up to tens of seconds. Typical somatic and neurite sparks were of 0.3- and 0.52-fold increase in local fluo-4 fluorescence, respectively. Typical Ca2+ glows were brighter ( F/Fo^O.6), but were highly confined in space. The half maximum of full duration of neurite sparks was much longer than those in the soma (685 versus 381 ms).Conclusion: Co-existence of Ca2+ sparks and Ca2+ glows in SCG neurons indicates distinctive local regulation of Ca2+ release kinetics. The local Ca2+ signals of variable, site-specific temporal length may bear important implications in encoding a "memory" of the trigger signal.