Calcium channel current in rat dental pulp cells

Voltage-gated Ca(2+) currents in early-passage rat dental pulp cells were studied using whole-cell patch-clamp techniques. With Ba(2+) 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. I(f) was activated by membrane depolarizations more positive than -30 mV, and displayed fast inactivation kinetics, while I(s) was activated by steeper depolarizations and inactivated more slowly. At peak current, time constants of inactivation for I(f) and I(s) were approximately 17 vs. approximately 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 Ca(2+) channels. I(s) was also blocked by the peptide omega-Conotoxin GVIA. Taken together, results suggested that I(f) was mediated by divalent cation flow through voltage-gated T-type Ca(2+) channels, whereas I(s) was mediated by L- and N-type Ca(2+) channels in the pulp cell membrane. The expression of these prominent, voltage-gated Ca(2+) 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.