Osteoblasts derived from load-bearing bones of the rat express both L- andT-like voltage-operated calcium channels and mRNA for alpha(1C), alpha(1D)and alpha(1G) subunits

Voltage operated calcium channels (VOCCs) are implicated in osteoblastic me chano- and hormonal transduction. Very little, however, is known about the expression of VOCCs in osteoblasts of load-bearing bones. Here we describe two types of whole-cell calcium current in rat femoral explant-derived oste oblasts. The first is high-voltage activated and sensitive to nifedipine, B ay K8644 and FPL 64176. The second is low-voltage activated and is sensitiv e to micromolar concentrations of Ni2+. The properties of these two current s are consistent with those of L-type and T-type calcium currents respectiv ely. T-type currents were detected in most cells on the day of passage, the level of expression being significantly lower on subsequent days. L-type c urrents were also most common on the day of passage but were detected consi stently throughout the 4-day period of study. The reverse transcription pol ymerase chain reaction with non-specific primers directed against all L-typ e VOCC al subunits and then with specific primers directed against sequence s from rat brain alpha(1C) (L-type), alpha(1D) (L-type) and alpha(1G) (T-ty pe) VOCC subunits detected transcripts of appropriate size in all four case s. Products from the three sets of specific primer pairs (alpha(1C), alpha( 1D), alpha(1G)) were sequenced and were identical to their respective rat b rain templates.