Table 1.

Extracellular acidic pH effects on bone cells and the role of proton-sensing GPCRs and ion channels

Receptors	Bone cell types	Acidification conditions	Signalings and functions	Acidification-induced actions	Ref.
OGR1	Osteoblasts	pH 7.6–6.3	Gq/11/PLC/Ca2+	COX-2 expression, PGE2 production	[77]
	Osteoclasts	pH 7.6–7.0	Ca2+/calcineurin/NFATc1	Osteoclastogenesis and bone resorption	[78]
	Osteoclasts	pH 7.6, pH 7.0	Protein kinase	Osteoclast survival	[79]
GPR4	Osteoblasts	pH 8–6	cAMP accumulation	RANKL expression	[80]
TDAG8	Osteoblasts	pH 7.4–6.88	cAMP accumulation	N/A	[80]
	Osteoclasts	pH 7.4	cAMP accumulation	Inhibition of bone resorption	[81]
ASIC1-3	Osteoblasts	pH < 7	Proton channel	N/A	[82]
	Osteoclasts	pH < 7	Proton channel	Possible role in monocyte differentiation and osteoclast survival	[82]
TRPV1	Osteoblasts	pH 5–4	Proton channel	Osteoblast differentiation and function	[83]
TRPV1, 2, 4, 5	Osteoclasts	pH 5–4	Proton channel	Osteoclast differentiation and function	[83, 84]