title: Decreased potassium stimulates bone resorption.
abstract: Metabolic acidosis induces net calcium efflux (JCa+) from cultured bone, in part, through an increase in osteoclastic resorption and a decrease in osteoblastic formation. In humans provision of base as potassium (K+) citrate, but not sodium (Na+) citrate, reduces urine Ca (UCa), and oral KHCO3 decreases bone resorption and UCa in postmenopausal women. Potassium deprivation alone leads to an increase in UCa. To determine whether decreased extracellular K+ concentration ([K+]) at a constant pH, PCO2, and [HCO-3] alters JCa+ and bone cell activity, we measured JCa+, osteoblastic collagen synthesis, and osteoclastic beta-glucuronidase release from neonatal mouse calvariae cultured for 48 h in medium of varying [K+]. Calvariae were cultured in control medium (approximately 4 mM [K+]) or medium with mildly low K+ (MLK, approximately 3 mM [K+]), very low K+ (VLK, approximately 2 mM [K+]), or extremely low K+ (ELK, approximately 1 mM [K+]) (n > or = 9 in each group). Compared with control, ELK, but not MLK or VLK, resulted in a marked increase in JCa+ and an increase in beta-glucuronidase release and a decrease in collagen synthesis. JCa+ was correlated directly with medium beta-glucuronidase activity and inversely with collagen synthesis. To determine whether the reduction in medium [K+] was associated with a decrease in intracellular pH (pHi), we measured pHi in MC3T3-E1 cells, a mouse osteoblastic cell line. Incubation in 1 mM [K+] led to a significant decrease in pHi compared with 3 mM [K+]. Thus incubation in a reduced [K+] medium stimulates JCa+ and osteoclastic enzyme release and inhibits osteoblastic collagen synthesis, which may be mediated by a reduction in bone cell pH.
authors.affiliation: Department of Medicine, University of Rochester School of Medicine, New York 14642, USA.
authors.forename: D A
authors.initials: DA
authors.lastname: Bushinsky
authors.forename: D R
authors.initials: DR
authors.lastname: Riordon
authors.forename: J S
authors.initials: JS
authors.lastname: Chan
authors.forename: N S
authors.initials: NS
authors.lastname: Krieger
mesh_terms: D000818:Animals; D001862:Bone Resorption / Q000503:physiopathology*; D002118:Calcium / Q000378:metabolism; D003094:Collagen / Q000096:biosynthesis; D003470:Culture Media / Q000378:metabolism; D005966:Glucuronidase / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007425:Intracellular Membranes / Q000378:metabolism; D051379:Mice; D008815:Mice, Inbred Strains; D009924:Organ Culture Techniques; D010006:Osteoblasts / Q000378:metabolism; D010010:Osteoclasts / Q000201:enzymology; D011188:Potassium / Q000378:metabolism*; D012886:Skull / Q000166:cytology / Q000378:metabolism
chemical_list: D003470:Culture Media; D003094:Collagen; D005966:Glucuronidase; D011188:Potassium; D002118:Calcium