THE REGULATION OF PH(I) IN OSTEOCLASTS IS DEPENDENT ON THE CULTURE SUBSTRATE AND ON THE STAGE OF THE RESORPTION CYCLE

The present study was performed to clarify the role of vacuolar H+-ATP ase in the regulation of the intracellular pH (pH(i)) in osteoclasts. Bafilomycin A(1) or amiloride were added to rat osteoclast cultures to block the H+-ATPases and Na+/H+-exchangers, respectively. Addition of 10(-8) M bafilomycin A(1) to osteoclasts cultured on bone induced a r apid decrease of the pH(i), while addition of amiloride had only a mim er effect. The response to bafilomycin A(1) appeared simultaneously wi th resorption activity and was abolished when resorption;ion was inhib ited by calcitonin., Osteoclasts on bone recovered from acid loading c aused by propionate in the presence of amiloride, while bafilomycin A( 1) inhibited this recovery almost completely, The pH(i) of osteoclasts cultured on glass responded to the addition of amiloride, but was not effected by even high concentrations of bafilomycin A(1). In contrast , as little as 10(-10) M bafilomycin A(1) caused accumulation of large vesicles in the cytoplasm. (C) 1997 Academic Press.