ENZYME CYTOCHEMICAL EXPRESSION OF AORTIC SMOOTH-MUSCLE CELL MODULATION IN PRIMARY AND SECONDARY CULTURES

''Contractile'' arterial smooth muscle cells (SMC) return to a less di fferentialed ''synthetic'' state during adaptative and proliferative p rocesses in vitro and in cell cultures. At present, the enzyme express ion of the modulation of cultured SMC is partially unknown. In order t o de ne 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. Th e ''contractile'' SMC in aorta of 2 months old rat showed very high nu cleotide hydrolase activities (5'-nucleotidase, Mg-ATPase, Ca-ATPase), and naphtylesterase activities and weak lysosomal acid phosphatase ac tivity; the glycolysis-linked dehydrogenases were expressed with highe r activities than Krebs cycle-linked enzymes. In primary cultures, the SMC near the explant expressed a ''contractile-like'' enzyme behaviou r, in opposite to cells in the peripheral part of growing area enzymat ically similar to sub-cultured SMC. Proliferating SMC in secondary cul tures were characterized by increased lysosomal activities and by the decrease or disappearance of Ca-ATPase, Mg-ATPase, 5'-nucleotidase, an d butyrylcholinesterase activities like fetal SMC in vivo. These enzym e changes in subcultures might be related to a deficiency of nucleotid e ester hydrolysis, abnormal adenosine and AMP levels, lowered lipolyt ic capability and increased lysosomal reactivity. In conclusion, subcu ltured ''synthetic'' SMC expressed enzyme cytochemical patterns differ ent from those of ''contractile'' SMC and similar to those of fetal im mature SMC. Their enzyme behaviour is unfavourable to contractile func tion and favourable to cell proliferation and lipid accumulation, two characteristic features of SMC in atherosclerotic plaques.