Calcium channel current in rat dental pulp cells

Voltage-gated Ca2+ currents in early-passage rat dental pulp cells were studied using whole-cell patch-clamp techniques. With Ba2+ as the charge carrier, two prominent inwardly-directed currents, I-f and I-s, were identified in these cells that could be distinguished on the basis of both kinetics and pharmacology. Is was activated by membrane depolarizations more positive than -30 mV, and displayed fast inactivation kinetics, while I, was activated by steeper depolarizations and inactivated more slowly. At peak current, time constants of inactivation for I-f and I-s were similar to 17 vs. similar to 631 msec. Both I-f and I-s could be blocked by lanthanum. By contrast, only I-s was sensitive to either Bay-K or nifedipine, a specific agonist and antagonist, respectively, of L-type Ca2+ channels. I, was also blocked by the peptide omega-Conotoxin GVIA. Taken together, results suggested that If was mediated by divalent cation flow through voltage-gated T-type Ca2+ channels, whereas I, was mediated by L- and N-type Ca2+ channels in the pulp cell membrane. The expression of these prominent, voltage-gated Ca2+ channels in a presumptive mineral-inductive phenotype suggests a functional significance vis a vis differentiation of dental pulp cells for the expression and secretion of matrix proteins, and/or formation of reparative dentin itself.