Ca2+ sparks and Ca2+ glows in superior cervical ganglion neurons.

Aim: Ca²⁺ release from the endoplasmic reticulum (ER) is an integral component of neuronal Ca²⁺ signaling. The present study is to investigate properties of local Ca²⁺ release events in superior cervical ganglion (SCG) neurons. Methods: 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. Results: Two populations of local Ca²⁺ release events with distinct temporal characteristics were evoked by 1.5 mmol/L caffeine near the surface membrane in the soma and the neurites of SCG neurons. Brief events similar to classic Ca²⁺ 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 (Δ F/F₀ approximately 0.6), but were highly confined in space. The half maximum of full duration of neurite sparks was much longer than those in the soma (685 vs 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. [ABSTRACT FROM AUTHOR]