[The dynamics of two types of tyrosine protein kinases in the proliferation of cultivated vascular smooth muscle cells].

We have studied the membrane-bound tyrosine protein kinases (TPK) in cultivated aortic smooth muscle cells (ASMC) from the rabbit, and found that the cytosolic (membranous)TPK and the nuclear (membranous)TPK are two distinctive types of isozymes as judged by criteria on dynamics: (1) using synthetic poly(Glu. Ala. Tyr)n(6:3:1) as a substrate, the relative extents of stimulation by Mn2+ (450%) was more effective than that by Mg2+ (100%) on cytosolic TPK, but Mn2+ was less effective (100%) than Mg2+ (130%) on nuclear TPK: (2) the concentrations of Mn2+ and Mg2+ giving maximal stimulation on cytosolic TPK were 15 mmol/L and 50 mmol/L, whereas on nuclear TPK were 1 mmol/L and 5 mmol/L, respectively. These results indicate that the attitudes toward Mn2+ and Mg2+ can distinguish the cytosolic TPK from the nuclear one. In nucleus, with the entry of ASMC from G0 to G1 stage, TPK activity increased rapidly and reached the peak (12 times G0 activity) at the early G1 stage (3 hrs from G0), then decreased dramatically to basic line, and remained at a lower level thereafter. In cytosol, the TPK activity decreased with the entry of ASMC from G0 to G1 stage and reached its lowest point at the middle of G1 stage (6 hrs from G0), and then increased with a transient peak at the late G1 stage (9 hrs). It went down to G0 level before DNA synthesis.