Different properties of caffeine-sensitive Ca²⁺ stores in peripheral and central mammalian neurones

Using indo-1 based microfluorometry for measuring the cytoplasmic free calcium concentration ([Ca²⁺]_i), the properties of caffeine-induced Ca²⁺ release from internal stores were studied in rat cultured central and peripheral neurones, including dorsal root ganglia (DRG) neurones, neurones from nucleus cuneatus, CA1 and CA3 hippocampal region and pyramidal neocortical neurones. Under resting conditions the Ca²⁺ content of internal stores in DRG neurones was high enough to produce caffeine-triggered [Ca²⁺]_i transients. Caffeine-induced Ca²⁺ release depleted internal stores in DRG neurones, but they refilled themselves spontaneously up to 81.4±5.67 % within 10 minutes. In contrast, in all types of central neurones the resting Ca²⁺ content of internal stores was low, but the stores could be charged by transmembrane Ca²⁺ influx through voltage-operated calcium channels. After charging, the stores in central neurones spontaneously lost releasable calcium content and within 10 minutes they emptied again. We suggest that in sensory neurones calcium stores are continuously filled by releasable calcium and after discharge they can refill themselves spontaneously, while in central neurones internal calcium stores can be charged by releasable calcium only transiently.