Expression of mRNAs for the α1 subunit of voltage-gated calcium channels in human osteoblast-like cell lines and in normal human osteoblasts

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 alpha(1) subunit of voltage-gated calcium channels have been cloned including L-type (alpha(1S), alpha(1C) and alpha(1D)) and non-L-type (alpha(1A), alpha(1B), and alpha(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 alpha(1) 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 (alpha(1C) and alpha(1A)), three isoforms were variably expressed (alpha(1S), alpha(1D) and alpha(1B)), and one isoform was not expressed in any of the osteoblast-like cells (alpha(1E)) but was easily detected in human brain controls. Our results indicate that mRNAs for multiple calcium channel alpha(1) 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.