Inhibition of Ca2+ uptake into A7r5 vascular smooth muscle cells by farnesol: lack of effect on membrane fluidity and Ca2+-ATPase activities.
BACKGROUND
Previous studies have shown that farnesol, a 15-carbon nonsterol derivative of mevalonic acid, inhibits vasoconstriction. Because of its lipophilic properties, we hypothesized that farnesol increased membrane dynamics, thus reducing uptake of Ca2+ and contraction.


OBJECTIVE
To characterize the effect of farnesol on cell membrane fluidity.


METHODS
The study was conducted using A7r5 cells, a rat aortic vascular smooth muscle cell line. Inhibition of Ca2+ uptake by farnesol was first established in these cells. Then, the effect of farnesol on membrane dynamics was determined. Finally, to ascertain that activation of Ca2+ extrusion and reuptake processes by farnesol did not occur, Ca2+-ATPase activity was examined.


METHODS
Membrane fluidity in cell homogenates was estimated using two fluorescent dyes (1,6-diphenyl-1,3,5-hexatriene) and (1-[-(trimethylamino)-phenyl]-6-phenyl-1,3,5-hexatriene). Ca2+ uptake was determined by monitoring the changes in cytosolic Ca2+ concentration ([Ca2+]i) in fura-2-loaded cells after addition of KCI. Ca2+-ATPase activity was measured in 100000 x g cell fractions.


RESULTS
Farnesol reduced KCI-induced (Ca2+]i transients significantly (P < 0.001), but did not modify membrane dynamic properties [0.214+/-0.007 versus 0.218+/-0.007 (n = 10) and 0.142+/-0.002 versus 0.146+/-0.003 (n = 5) for 1 -[-(trimethylamino)-phenyl]-6-phenyl-1,3,5-hexatriene and 1,6-diphenyl-1,3,5-hexatriene anisotropies, respectively; NS]. Administration of up to 30 micromol/l farnesol did not affect Ca2+-ATPase activity.


CONCLUSIONS
Farnesol inhibits KCI-dependent rise of [Ca2+]i in A7r5 cells. This effect of farnesol is not related to a global change in plasma membrane lipid organization or to activation of Ca2+ pumps. Other mechanisms such as direct inhibition of voltage-dependent Ca2+ channels could therefore explain the biologic action of farnesol in the vascular tissue.
Roullet
J B
JB
Department of Nephrology, Hypertension and Clinical Pharmacology, Oregon Sciences Health University, Portland 97201, USA.
Le Quan Sang
K H
KH
Luft
U
U
Watanabe
M
M
Otsuka
K
K
McCarron
D A
DA
Devynck
M A
MA
D000818:Animals; D001011:Aorta / Q000166:cytology; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D002417:Cattle; D002460:Cell Line; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D004161:Diphenylhexatriene / Q000031:analogs & derivatives; D004305:Dose-Response Relationship, Drug; D005204:Farnesol / Q000494:pharmacology*; D005454:Fluorescence Polarization; D005456:Fluorescent Dyes; D008560:Membrane Fluidity / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D011189:Potassium Chloride / Q000494:pharmacology; D051381:Rats; D013050:Spectrometry, Fluorescence
D005456:Fluorescent Dyes; D004161:Diphenylhexatriene; D005204:Farnesol; D011189:Potassium Chloride; C033628:1-(4-(trimethylamino)phenyl)-6-phenylhexa-1,3,5-triene; D000252:Calcium-Transporting ATPases; D002118:Calcium