Enamel cells positively respond to agonist-induced activation of Ca²⁺

Objectives: Background: We have recently reported that enamel cells stimulated with thapsigargin show an increase in cytosolic Ca²⁺ concentration ([Ca²⁺]_c) via store depletion followed by Ca²⁺ entry consistent with store-operated Ca²⁺ entry (SOCE). We also showed that in enamel cells pre-treated with Ca²⁺ release activated Ca²⁺ (CRAC) channel inhibitors resulted in a significant decrease in Ca²⁺ entry. CRAC channels are important Ca²⁺ influx mechanism in many cell types, as well as for enamel formation as disruptions to the normal functioning of this channel result in amelogenesis imperfecta-like phenotypes.
Aim: To identify potential agonists involved in cytosolic Ca²⁺ modulation and also possible CRAC channel activators in enamel cells, we investigated cell responses to common physiological agonists such as cholecystokinin (CCK8), serotonin, ATP and acetylcholine, in rat enamel organ cells.
Methods: To determine [Ca²⁺]_c, isolated enamel organ cells were loaded with Fura-2/AM and fluorescence measurements were made using spinning disk confocal microscopy. [Ca²⁺]_c was measured prior to and following addition of CCK8, serotonin, ATP and acetylcholine to the Ringer solution.
Results: We found that acute expose of enamel cells to CCK, serotonin, ATP and acetylcholine resulted in a rapid increase in [Ca²⁺]_c which was due to Ca²⁺ release from intracellular stores and influx of extracellular Ca²⁺ across the cell membrane consistent with SOCE activity.
Conclusions: These data suggest that physiological agonists known to be involved with CRAC channel activation as well as agonist-mediated stimulation of [Ca²⁺]_c increase in other epithelial cells also appear to positively mediate Ca²⁺ influx in enamel cells. These data also imply the possibility of using pharmacological compounds to modulate of Ca²⁺ activity in enamel cells.