INHIBITION OF PROTEIN-KINASE-C ACTIVITY AND VASCULAR SMOOTH-MUSCLE CELL-GROWTH BY D-ALPHA-TOCOPHEROL

The inhibition by d-alpha-tocopherol of protein kinase C activity has been studied in synchronised A7r5 rat smooth muscle cells during the c ell cycle. Cell protein kinase C activity has been found to oscillate, with a minimum in the G(0) phase, a maximum in the late G(1) phase an d a new minimum in the S phase. An inhibition of protein kinase C acti vity by d-alpha-tocopherol appears to be at the basis of cell growth i nhibition. Nevertheless, the amount of the different protein kinase C isoenzymes present in smooth muscle cells, measured by their specific antibodies, does not change during the cell cycle in both untreated an d d-alpha-tocopherol-treated cells. The possible mechanisms of protein kinase C modulation during the cell cycle and of its inhibition by d- alpha-tocopherol are discussed.