Expression of mRNAs for the α₁ Subunit of Voltage-Gated Calcium Channels in Human Osteoblast-Like Cell Lines and in Normal Human Osteoblasts

Abstract.

The activation of osteoblast calcium channels by many bone regulatory factors suggests an important role for intracellular calcium signaling in the control of bone remodeling. At least six different genes for the α₁ subunit of voltage-gated calcium channels have been cloned including L-type (α_1S, α_1C, and α_1D) and non-L-type (α_1A, α_1B, and α_1E) isoforms. The goal of the present study was to identify which of these calcium channel isoforms are transcribed in human osteoblast-like cell lines (hFOB, MG-63, SAOS-2, TE-85, G-292) and in cultures of normal human osteoblasts. Reverse transcriptase-PCR was used to amplify sequences corresponding to each of the α₁ subunits using isoform specific primers. The products of the PCR reaction were cloned and sequenced to verify their identity and used to probe southern blots of the PCR reactions. The results indicate that among the different types of osteoblast-like cells examined, two calcium channel isoforms were always expressed (α_1C and α_1A), three isoforms were variably expressed (α_1S, α_1D and α_1B), and one isoform was not expressed in any of the osteoblast-like cells (α_1E) but was easily detected in human brain controls. Our results indicate that mRNAs for multiple calcium channel α₁ subunits are expressed in human osteoblasts, including both L-type and non-L-type isoforms. In addition, significant heterogeneity exists between the different osteoblast cell models examined in the type and mRNA abundance of the different calcium channel isoforms.