CYCLIC STRAIN STIMULATES DEPHOSPHORYLATION OF THE 20KDA REGULATORY MYOSIN LIGHT-CHAIN IN VASCULAR SMOOTH-MUSCLE CELLS

The role of cyclic strain in the regulation of 20 kDa myosin light cha in phosphorylation (MLC20) in cultured smooth muscle cells (SMC) is un known. The objective of this study was to determine whether cyclic str ain stimulates the dephosphorylation of MLC20 in serum-fed SMC display ing a high basal level of phosphorylation. Confluent bovine aortic SMC were subjected to 10% average strain at 60 cycles per minute for 30 a nd 60 minutes. Basal MLC20 phosphorylation (N=non,M=mono,D=di) of seru m-fed SMC was as follows: N=34%:M=27%:D=39%, After 60 min of cyclic st rain, both mono and diphosphorylated MLC20 were decreased to 21 and 15 %, respectively. The strain-induced dephosphorylation of MLC20 was par tially inhibited by the protein phosphatase 1/2A inhibitor, calyculin A (5 nM). However, phosphorylase a phosphatase activities in Triton-so luble and insoluble fractions of SMC were unaffected by cyclic strain. The data suggest that cyclic strain causes dephosphorylation of MLC20 in SMC which may be partially due to activation of MLC20 phosphatase and/or inhibition of MLC20 phosphorylation. (C) 1994 Academic Press, I nc.