Relaxin treatment alters the kinetic properties of myosin light chain kinase activity in rat myometrial cells in culture

Endocrinology
C J Hsu, B M Sanborn

Abstract

Relaxin treatment altered the kinetic properties of rat myometrial cell myosin light chain kinase (MLCK) by increasing the K50 of the enzyme for calmodulin (CaM) from 1.1 +/- 0.1 to 38 +/- 14 nM. When MLCK was assayed in the presence of 7 nM CaM to maximize the effect of the decreased affinity for CaM between control and relaxin-treated groups, a rapid concentration-dependent effect of the hormone was observed. Relaxin decreased MLCK activity significantly within 1 min. The ED50 of the effect was 0.4 microgram/ml. In addition to its effect on Ca2+-CaM-dependent activity, relaxin also decreased Ca2+-CaM-independent MLCK activity. This decrease was not attributable to a decrease in the affinity of the enzyme for myosin. There was a temporal association between the effects of relaxin on mean cell length, elevation of cAMP levels in the presence of 0.4 microM forskolin previously shown in other studies, and the alteration of MLCK activity. All three parameters were changed significantly within 1 min after exposure to relaxin. The ED50 of relaxin for cell shape changes, cAMP elevation, and effects on MLCK activity were all approximately 0.4 microgram/ml. Relaxin may act in part by a cAMP-mediated phosphorylation of MLCK, thereby dec...Continue Reading

Citations

Apr 1, 1990·In Vitro Cellular & Developmental Biology : Journal of the Tissue Culture Association·M PhillippeS Bangalore
Mar 26, 2009·Archives of Gynecology and Obstetrics·Dunja M Baston-BüstUlrike K Friebe-Hoffmann
Oct 24, 2006·Regulatory Peptides·Ulrike Friebe-HoffmannPhillip N Rauk
Oct 21, 2000·Endocrine Reviews· Challis JRGS J Lye

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