Regulation of expressed truncated smooth muscle myosins. Role of the essential light chain and tail length.

Vascular tone, an important determinant of systemic vascular resistance and thus blood pressure, is affected by vascular smooth muscle (VSM) contraction. Key signaling pathways for VSM contraction converge on phosphorylation of the regulatory light chain (RLC) of smooth muscle myosin. This phosphorylation is mediated by Ca2+/calmodulin-dependent myosin light chain kinase (MLCK) but Ca2+-independent kinases may also contribute, particularly in sustained contractions. Signaling through MLCK has been indirectly implicated in maintenance of basal blood pressure, whereas signaling through RhoA has been implicated in salt-induced hypertension. In this report, we analyzed mice with smooth muscle-specific knockout of MLCK. Mesenteric artery segments isolated from smooth muscle-specific MLCK knockout mice (MLCKSMKO) had a significantly reduced contractile response to KCl and vasoconstrictors. The kinase knockout also markedly reduced RLC phosphorylation and developed force. We suggest that MLCK and its phosphorylation of RLC are required for tonic VSM contraction. MLCKSMKO mice exhibit significantly lower basal blood pressure and weaker responses to vasopressors. The elevated blood pressure in salt-induced hypertension is reduced below normotensive levels after MLCK attenuation. These results suggest that MLCK is necessary for both physiological and pathological blood pressure. MLCKSMKO mice may be a useful model of vascular failure and hypotension.

Download Full-text

Deletion of 1–43 amino acids in cardiac myosin essential light chain blunts length dependency of Ca2+ sensitivity and cross-bridge detachment kinetics

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.00572.2012 ◽

2013 ◽

Vol 304 (2) ◽

pp. H253-H259 ◽

Cited By ~ 14

Author(s):

John Jeshurun Michael ◽

Sampath K. Gollapudi ◽

Steven J. Ford ◽

Katarzyna Kazmierczak ◽

Danuta Szczesna-Cordary ◽

...

Keyword(s):

Amino Acids ◽

Light Chain ◽

Sarcomere Length ◽

Cardiac Myosin ◽

Wild Type ◽

Essential Light Chain ◽

Cross Bridge ◽

Maximal Activation ◽

Cardiac Muscle Fibers

The role of cardiac myosin essential light chain (ELC) in the sarcomere length (SL) dependency of myofilament contractility is unknown. Therefore, mechanical and dynamic contractile properties were measured at SL 1.9 and 2.2 μm in cardiac muscle fibers from two groups of transgenic (Tg) mice: 1) Tg-wild-type (WT) mice that expressed WT human ventricular ELC and 2) Tg-Δ43 mice that expressed a mutant ELC lacking 1–43 amino acids. In agreement with previous studies, Ca2+-activated maximal tension decreased significantly in Tg-Δ43 fibers. pCa50 (−log10 [Ca2+]free required for half maximal activation) values at SL of 1.9 μm were 5.64 ± 0.02 and 5.70 ± 0.02 in Tg-WT and Tg-Δ43 fibers, respectively. pCa50 values at SL of 2.2 μm were 5.70 ± 0.01 and 5.71 ± 0.01 in Tg-WT and Tg-Δ43 fibers, respectively. The SL-mediated increase in the pCa50 value was statistically significant only in Tg-WT fibers ( P < 0.01), indicating that the SL dependency of myofilament Ca2+ sensitivity was blunted in Tg-Δ43 fibers. The SL dependency of cross-bridge (XB) detachment kinetics was also blunted in Tg-Δ43 fibers because the decrease in XB detachment kinetics was significant ( P < 0.001) only at SL 1.9 μm. Thus the increased XB dwell time at the short SL augments Ca2+ sensitivity at short SL and thus blunts SL-mediated increase in myofilament Ca2+ sensitivity. Our data suggest that the NH2-terminal extension of cardiac ELC not only augments the amplitude of force generation, but it also may play a role in mediating the SL dependency of XB detachment kinetics and myofilament Ca2+ sensitivity.

Download Full-text