Isoforms of Na+,K+-ATPase in primary human bone derived osteoblasts

Osteoblasts play a critical role in bone formation and mineralization, a process that depends on optimal calcium and phosphate homeostasis. Transcellular transport of free calcium [Ca2+], uptake of inorganic phosphate (P(i)) and numerous other transport systems in osteoblasts depend on a low intracellular Na+:K+ ratio furnished by (Na++K+)-stimulated adenosine triphosphatase (Na+,K+-ATPase), an enzyme embedded in the plasma membrane. In this study, we have examined, for the first time, the expression of the catalytic α and regulatory β subunit isoforms of Na+,K+-ATPase in primary human bone derived osteoblasts using isoform specific monoclonal and polyclonal antibodies. Immunofluorescence was used to detect the α1, β1 and β2 isoforms of Na+,K+-ATPase in dispersed osteoblasts. Laser scanning confocal microscopy also revealed an abundance of Na+,K+-ATPase isoforms in subcellular compartments. The existence of α1, β1 and β2 suggests that at least two major isozyme combinations of Na+,K+-ATPase are present in human bone (α1β1,α1β2)