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 chain phosphorylation (MLC20) in cultured smooth muscle cells (SMC) is unknown. The objective of this study was to determine whether cyclic strain stimulates the dephosphorylation of MLC20 in serum-fed SMC displaying a high basal level of phosphorylation. Confluent bovine aortic SMC were subjected to 10% average strain at 60 cycles per minute for 30 and 60 minutes. Basal MLC20 phosphorylation (N=non,M=mono,D=di) of serum-fed SMC was as follows: N=34%:M=27%:D=39%, After 60 min of cyclic strain, both mono and diphosphorylated MLC20 were decreased to 21 and 15%, respectively. The strain-induced dephosphorylation of MLC20 was partially inhibited by the protein phosphatase 1/2A inhibitor, calyculin A (5 nM). However, phosphorylase a phosphatase activities in Triton-soluble 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, Inc.