Distribution of Inositol 1,4,5-Trisphosphate Receptors in Rat Osteoclasts

Inositol 1,4,5-trisphosphate (IP(3)) receptors (IP(3)Rs) are Ca(2+) channels that localize to intracellular Ca(2+) stores such as the endoplasmic reticulum (ER). Recently, IP(3)Rs were found to participate in the formation of the cytoskeleton and cellular adhesions. In this study, we examined the cellular localization of type I, II, and III IP(3)Rs to assess their role in cellular adhesion in rat osteoclasts. Rat bone marrow cells were cultured in α-MEM with 10% fetal bovine serum, M-CSF, RANKL, and 1,25(OH)(2)D(3) for 1 week to promote osteoclast formation. Type I, II, and III IP(3)R expression in the osteoclasts was then examined by RT-PCR. Double-staining was performed using antibodies against type I, II, and III IP(3)Rs and DiOC(6), an ER marker, or TRITC-phalloidin, an actin filament marker. Expression of all three IP(3)Rs was detected in the newly formed osteoclasts; however, the localization of the type I and II IP(3)Rs was predominantly close to nuclear, and possibly colocalized with the ER, while the type III IP(3)Rs were localized to the ER and podosomes, actin-rich adhesion structures in osteoclasts. These findings suggest that type III IP(3)Rs are associated with osteoclast adhesion.