Parathyroid hormone enhances fluid shear-induced [Ca2+](i) signaling in osteoblastic cells through activation of mechanosensitive and voltage-sensitive Ca2+ channels
Kd. Ryder et Rl. Duncan, Parathyroid hormone enhances fluid shear-induced [Ca2+](i) signaling in osteoblastic cells through activation of mechanosensitive and voltage-sensitive Ca2+ channels, J BONE MIN, 16(2), 2001, pp. 240-248
Osteoblasts respond to both fluid shear and parathyroid hormone (PTH) with
a rapid increase in intracellular calcium concentration ([Ca2+](i)). Becaus
e both stimuli modulate the kinetics of the mechanosensitive cation channel
(MSCC), we postulated PTH would enhance the [Ca2+](i) response to fluid sh
ear by increasing the sensitivity of MSCCs. After a 3-minute preflow at 1 d
yne/cm(2), MC3T3-E1 cells were subjected to various levels of shear and cha
nges in [Ca2+](i) were assessed using Fura-2. Pretreatment with 50 nM bovin
e PTH(1-34) [bPTH(1-34)] significantly enhanced the shear magnitude-depende
nt increase in [Ca2+](i). Gadolinium (Gd3+), an MSCC blocker, significantly
inhibited the mean peak [Ca2+](i) response to shear and sheer + bPTH(1-34)
. Nifedipine (Nif), an L-type voltage-sensitive Ca2+ channel (VSCC) blocker
, also significantly reduced the [Ca2+](i) response to shear + bPTH(1-34),
but not to shear alone, suggesting VSCC activation plays an interactive rol
e in the action of these stimuli together. Activation of either the protein
kinase C (PKC) or protein kinase A. (PKA) pathways with specific agonists
indicated that PKC activation did not alter the Ca2+ response to shear, whe
reas PKA. activation significantly increased the [Ca2+](i), response to low
er magnitudes of shear, bPTH(1-34), which activates both pathways, induced
the greatest [Ca2+](i) response at each level of shear, suggesting an inter
action of these pathways in this response. These data Indicate that PTH sig
nificantly enhances the [Ca2+](i) response to shear primarily via PKA modul
ation of the MSCC and VSCC.