Use of amine buffers for in vitro studies of bone resorption

Responses of cultured fetal rat bones to parathyroid hormone (PTH) were compared in media gassed with 5% CO₂ and buffered with bicarbonate or in media buffered with the amine buffers HEPES (N-2-hydroxyethylpiperazine-N′-2-ethanesulfonic acid), TES (N-tris(hydroxymethyl)methyl-2-aminoethanesulfonic acid), PIPES (piperazine-N,N′-bis(2-ethanesulfonic acid)), Tris (tris(hydroxymethyl)aminomethane), or glycylglycine. PTH-induced bone resorption was markedly reduced in media buffered with the amine buffers and cultured in air in the absence of added bicarbonate. When the amine buffers were added to bicarbonate-buffered media, they decreased the responses of the bones to submaximal concentrations of PTH. But the response to supramaximal concentrations of PTH was usually not impaired. The results confirm our earlier studies indicating a CO₂ and/or bicarbonate requirement for optimal bone resorption. They also demonstrate that the amine buffers can inhibit the responses of bone to PTH even in the presence of CO₂ and bicarbonate.