NCX3 is a major functional isoform of the sodium-calcium exchanger in osteoblasts.
The calcium phosphate-based skeleton of vertebrates serves as the major reservoir for metabolically available calcium ions. The skeleton is formed by osteoblasts which first secrete a proteinaceous matrix and then provide Ca++ for the calcification process. The two calcium efflux ports found in most cells are the plasma membrane Ca-ATPase (PMCA) and the sodium-calcium exchanger (NCX). In osteoblasts, PMCA and NCX are located on opposing sides of the cell with NCX facing the mineralizing bone surface. Two isoforms of NCX have been identified in osteoblasts NCX1, and NCX3. The purpose of this study was to determine the extent to which each of the two NCX isoforms support delivery of Ca++ into sites of calcification and to discern if one could compensate for the other. SiRNA technology was used to knockdown each isoform separately in MC3T3-E1 osteoblasts. Osteoblasts in which either NCX1 or NCX3 was impaired were tested for Ca++ efflux using the Ca++ specific fluorophore, fluo-4, in a sodium-dependent calcium uptake assay adapted for image analysis. NCX3 was found to serve as a major contributor of Ca++ translocation out of osteoblasts into calcifying bone matrix. NCX1 had little to no involvement.
The Pennsylvania State University, Department of Biochemistry and Molecular Biology, University Park, Pennsylvania 16802, USA. dms28@psu.edu
Donna M
DM
Sosnoski
Carol V
CV
Gay
D016475:3T3 Cells; D000818:Animals; D001693:Biological Transport, Active; D001857:Bone Matrix / Q000502:physiology; D002113:Calcification, Physiologic; D002118:Calcium / Q000502:physiology*; D002460:Cell Line; D002462:Cell Membrane / Q000502:physiology; D026901:Membrane Transport Proteins / Q000502:physiology*; D051379:Mice; D010006:Osteoblasts / Q000502:physiology*; D053499:Plasma Membrane Calcium-Transporting ATPases / Q000502:physiology; D020033:Protein Isoforms / Q000235:genetics / Q000502:physiology; D019831:Sodium-Calcium Exchanger / Q000235:genetics / Q000502:physiology*
D026901:Membrane Transport Proteins; C499849:NCX1 protein, mouse; D020033:Protein Isoforms; C491101:Slc8a3 protein, mouse; D019831:Sodium-Calcium Exchanger; D053499:Plasma Membrane Calcium-Transporting ATPases; D002118:Calcium