Calcium-dependent second-messenger regulation of low-density lipoprotein oxidation by human aortic smooth muscle cells.
BACKGROUND
We postulated that the response of vascular smooth muscle cells (SMCs) to oxidized low-density lipoprotein (LDL) may be modulated through calcium and 3', 5' cyclic adenosine monophosphate (Ca+2-cAMP) second-messenger activity.


METHODS
Changes in cytosolic calcium [Ca+2]i in aortic SMCs exposed to native (N-) and oxidized (Ox-) LDL were measured with a Fura 2-AM indicator. The influence of cAMP on this response was determined by incubating the cells with either forskolin or 8-bromo-cAMP (stimulatory) or galanin (inhibitory). The cells were then activated by an initial preincubation with N- or Ox-LDL, and the subsequent cellular oxidation of N-LDL was measured. The effect of cAMP mediators alone or in conjunction with calcium antagonism was studied.


RESULTS
Exposure of SMCs to Ox-LDL resulted in a marked elevation of [Ca+2]i(306 +/- 12 nmol/L) compared with that in the control group (192 +/- 15 nmol/Liter; p < 10(-6)). This response was augmented by cAMP stimulation (406 +/- 8 nmol/L; p < 10(-6)) but reduced by cAMP inhibition (247 +/- 8 nmol/L; p < 10(-6)). The activation of intracellular signaling by initial Ox-LDL priming increased the subsequent oxidation of N-LDL (0.40 +/- 0.02 nmol malondialdehyde versus 0.24 +/- 0.02 nmol MDA control; p < 10(-4)). This response was enhanced by cAMP (0.45 +/- 0.03 nmol MDA; p < 10(-4)) and inhibited by galanin (0.26 +/- 0.02; p < 10(-4)). The cAMP effect was reversed by the blockade of calcium mobilization via membrane channels and reticular release.


CONCLUSIONS
Oxidized LDL-induced Ca+2-cAMP signaling modulates the cellular oxidation of N-LDL. This finding suggests a mechanism through which the scavenger uptake of modified LDL may potentially be regulated.
Wells
K E
KE
Case Western Reserve University, MetroHealth Medical Center, Cleveland, Ohio 44109, USA.
Alexander
J J
JJ
Miguel
R
R
D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D001011:Aorta / Q000166:cytology; D002118:Calcium / Q000032:analysis / Q000502:physiology*; D002478:Cells, Cultured / Q000187:drug effects / Q000502:physiology; D005576:Colforsin / Q000494:pharmacology; D003300:Copper / Q000502:physiology; D000242:Cyclic AMP / Q000502:physiology; D003600:Cytosol / Q000737:chemistry; D019004:Galanin / Q000494:pharmacology; D006801:Humans; D015227:Lipid Peroxidation / Q000187:drug effects / Q000502:physiology; D008077:Lipoproteins, LDL / Q000378:metabolism*; D009131:Muscle, Smooth, Vascular / Q000166:cytology*; D010084:Oxidation-Reduction; D015290:Second Messenger Systems / Q000187:drug effects / Q000502:physiology*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology
D008077:Lipoproteins, LDL; D005576:Colforsin; D015124:8-Bromo Cyclic Adenosine Monophosphate; D003300:Copper; D019004:Galanin; D000242:Cyclic AMP; D002118:Calcium