Cytosolic pH regulation in osteoblasts
Green, J.
Mineral and Electrolyte Metabolism 20(1-2): 16-30
1994
ISSN/ISBN: 0378-0392 PMID: 8202049 Document Number: 430919
The process of bone formation depends on an optimal alkaline pH in the extracellular milieu surrounding the osteoblast. To the extent that ionic composition of an extracellular environment is determined by events taking place inside the cell, it is conceivable that the pH in the fluid outside the osteoblast is affected by cytosolic pH (pHi) regulation by these cells. Under HEPES-buffered conditions, the main pH regulatory mechanism is the ubiquitous acid-extruding mechanism, Na+/H+ exchange. However, under the more physiologic HCO-3- environment, one can identify three additional acid-bone transporters; Na+-independent Cl-/HCO-3- exchanger, Na+ (HCO-3-)-3 cotransporter, and HCO-3--conductive pathway. In addition to their role in regulation of pHi in the osteoblast, these transporters also play a role in volume regulation of these cells both under hypertonic conditions (regulatory volume increase) and during osmotic swelling (regulatory volume decrease). Second messengers produced by calciotropic hormones (e.g. cytosolic Ca-2+, cAMP) regulate the activity of Na+/H+ exchanger and Cl-/HCO-3- exchanger.