Expression of CaV3.1 T-type Calcium Channels in Acutely Isolated Adult Rat Odontoblasts.

ABSTRACT

OBJECTIVE: Odontoblasts, which consist the outermost compartment of the dental pulp, are primarily engaged in dentin formation. Earlier evidence suggests that voltage-gated calcium channels, such as the high voltage-activated L-type calcium channels, serve as a calcium entry route to mediate dentin formation in odontoblasts. However, the involvement of other voltage-gated calcium channels in regulating intracellular Ca2+ remain unanswered. DESIGN: The expression of voltage-gated calcium channel subtypes of the P/Q- (CaV2.1), N-(CaV2.2), R- (CaV2.3), and T- (CaV3.1-3.3) type were screened in adult rat odontoblasts by single cell RT-PCR. Among these candidates, immunopositivity against CaV3.1 was examined in the odontoblastic layer in teeth sections and dissociated odontoblasts. To confirm the functional expression of CaV3.1 in odontoblasts, intracellular Ca2+ increase in response to membrane depolarization was monitored with Fura-2-based ratiometric calcium imaging. RESULTS: Among the candidate calcium channels, we found that mRNA for CaV3.1 is mainly detected in odontoblasts, with its expression being detected in the odontoblastic layer and dissociated odontoblasts. High extracellular K+-induced membrane depolarization was inhibited by pharmacological blockers for T-type calcium channels such as amiloride or ML218. CONCLUSION: Our results demonstrate that among P/Q-, N-, R-, and T-type calcium channels, CaV3.1 is mainly expressed in odontoblasts to mediate intracellular Ca2+ signaling in response to membrane depolarization. These findings suggest that CaV3.1 may facilitate intracellular Ca2+ dynamics especially in the range of subliminal depolarizations near resting membrane potentials where other high voltage-gated calcium channels such as the L-type are likely to be inactive.