Mb. Troyan et al., MITOCHONDRIAL-MEMBRANE POTENTIAL CHANGES IN OSTEOBLASTS TREATED WITH PARATHYROID-HORMONE AND ESTRADIOL, Experimental cell research, 233(2), 1997, pp. 274-280
This study assessed mitochondrial membrane potential changes in cultur
ed osteoblasts treated with hormones known to regulate osteoblasts., A
fluorescent carbocyanine dye, 5,5', 6,6'-tetrachloro-1,1', 3,3'-tetra
ethylbenzimidazolocarbocyanine iodide, also called JC-l, was used as a
probe. JC-l emits photons at 585 nm (orange-red) when the membrane po
tential in mitochondria is highly negative, but when the potential bec
omes reduced emission occurs at 527 nm (green). Osteoblasts were rinse
d in serum-free medium for 5 min, then loaded with 1 x 10(-6) M JC-l f
ar 10 min, The distribution and intensity of JC-l fluorescence were ev
aluated with a laser-scanning confocal microscope system. Hormone trea
tments included parathyroid hormone (PTH; 10(-8) M), 17 beta-estradiol
(10(-8) M), and thyroxine (T-4; 10(-8) M), The potassium ionophore va
linomycin (10(-6) M) was used as a control since it is known to disrup
t the electrochemical gradient of mitochondria without interfering wit
h the pH gradient. Valinomycin caused a profound, rapid increase (22.5
% above untreated values) in the green/red ratio, which indicated a lo
wering of the mitochondrial membrane potential in all samples evaluate
d. PTH caused a less pronounced, but significant (7-14%), reduction in
membrane potential in all cells examined, PTH is known to affect oste
oblasts in a number of ways and is inhibitory to mitochondrial respira
tion; the results confirm this effect. For estradiol, half of the cell
s responded at a significant level, with a membrane potential reductio
n of 6 to 13% being recorded; the other half did not respond. Thyroxin
e did not alter mitochondrial membrane potential. Responses were detec
table within 20 s for valinomycin, but occurred at a slower rate, over
200 to 300 s, following PTH and estradiol treatment. Responses to PTH
and estradiol could be due to mitochondrial uptake of cytosolic Ca2+.
(C) 1997 Academic Press.