Enzyme cytochemical expression of aortic smooth muscle cell modulation in primary and secondary cultures

"Contractile" arterial smooth muscle cells (SMC) return to a less differentiated "synthetic" state during adaptative and proliferative processes in vitro and in cell cultures. At present, the enzyme expression of the modulation of cultured SMC is partially unknown. In order to define metabolic events associated with cell modulation in vitro, we studied 16 enzyme activities in primary and secondary (P1-P3-P10) SMC cultures in comparison to in situ SMC in fetal and adult rat aorta. The "contractile" SMC in aorta of 2 months old rat showed very high nucleotide hydrolase activities (5'-nucleotidase, Mg-ATPase, Ca-ATPase), and naphthylesterase activities and weak lysosomal acid phosphatase activity; the glycolysis-linked dehydrogenases were expressed with higher activities than Krebs cycle-linked enzymes. In primary cultures, the SMC near the explant expressed a "contractile-like" enzyme behaviour, in opposite to cells in the peripheral part of growing area enzymatically similar to sub-cultured SMC. Proliferating SMC in secondary cultures were characterized by increased lysosomal activities and by the decrease or disappearance of Ca-ATPase, Mg-ATPase, 5'-nucleotidase, and butyrylcholinesterase activities like fetal SMC in vivo. These enzyme changes in subcultures might be related to a deficiency of nucleotide ester hydrolysis, abnormal adenosine and AMP levels, lowered lipolytic capability and increased lysosomal reactivity. In conclusion, subcultured "synthetic" SMC expressed enzyme cytochemical patterns different from those of "contractile" SMC and similar to those of fetal immature SMC. Their enzyme behaviour is unfavourable to contractile function and favourable to cell proliferation and lipid accumulation, two characteristic features of SMC in atherosclerotic plaques.