Osteoblasts derived from load-bearing bones of the rat express both L- and T-like voltage-operated calcium channels and mRNA for α1C, α1D and α1G subunits

Voltage operated calcium channels (VOCCs) are implicated in osteoblastic mechano- 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 osteoblasts. The first is high-voltage activated and sensitive to nifedipine, Bay K8644 and FPL 64176. The second is low-voltage activated and is sensitive to micromolar concentrations of Ni2+. The properties of these two currents are consistent with those of L-type and T-type calcium currents respectively. 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 currents were also most common on the day of passage but were detected consistently throughout the 4-day period of study. The reverse transcription polymerase chain reaction with non-specific primers directed against all L-type VOCC al subunits and then with specific primers directed against sequences from rat brain alpha(1C) (L-type), alpha(1D) (L-type) and alpha(1G) (T-type) VOCC subunits detected transcripts of appropriate size in all four cases. Products from the three sets of specific primer pairs (alpha(1C), alpha(1D), alpha(1G)) were sequenced and were identical to their respective rat brain templates.