Measurements of cytosolic free Ca2+ concentrations in odontoblasts.

To investigate the responsiveness of odontoblasts to electrical and mechanical stimuli, the concentrations of cytosolic free Ca2+ ([Ca2+]i) were measured using fura-2 microfluorometry in slice preparations of rat dental pulp. [Ca2+]i under resting conditions (basal [Ca2+]i) were 258.0 +/- 37.7 nM (mean +/- S.E., n = 113). The basal [Ca2+]i of the odontoblasts with remarkably active responses to stimuli were 221.0 +/- 81.1 nM (mean +/- S.E., range: 16-685 nM). Depolarization by high extracellular K+ concentration ([K+]o) caused a rapid increase in [Ca2+]i. The depolarization-induced increase in [Ca2+]i was enhanced by caffeine. The intense depolarization elicited [Ca2+]i oscillation in odontoblasts, which was enhanced by caffeine and suppressed by dantrolene. Hypotonic stimulation also induced an increase in [Ca2+]i of odontoblasts. The results indicate that the odontoblast possesses voltage-dependent Ca2+ channels, caffeine-sensitive Ca2+ stores and mechanosensitive cation channels.