Effect of Mg2+ on stress, myosin phosphorylation, and ATPase activity in detergent-skinned swine carotid media.
Smooth muscle contraction has a relatively high requirement for free magnesium (Mg2+). In this study we examined the effect of Mg2+ concentration ([Mg2+]) on Ca2+-dependent stress development and stress maintenance, myosin ATPase activity, and myosin light chain (MLC) phosphorylation levels in Triton X-100 detergent-skinned fibers of the swine carotid media. Increasing [Mg2+] in a stepwise fashion from 0.1 to 6 mM 1) decreased the magnitude and Ca2+ sensitivity of stress development but augmented the amount of stress maintained without proportional MLC phosphorylation, 2) produced a greater decrease in the Ca2+ sensitivity of MLC phosphorylation than that of stress development, and 3) decreased myosin ATPase activity. These findings demonstrate that Mg2+ differentially modulates the MLC phosphorylation-dependent development of stress and the MLC phosphorylation-independent maintenance of stress. We suggest that increases in [Mg2+] enhance stress maintenance by increasing [MgADP], thus increasing the number of cross bridges in a force-generating state, and by a direct effect on the pathway responsible for Ca2+-dependent, MLC phosphorylation-independent contractions.
D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002339:Carotid Arteries / Q000187:drug effects / Q000201:enzymology*; D002614:Chelating Agents / Q000494:pharmacology; D003902:Detergents; D004533:Egtazic Acid / Q000494:pharmacology; D008274:Magnesium / Q000494:pharmacology*; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000201:enzymology*; D018994:Myosin Light Chains / Q000378:metabolism*; D009218:Myosins / Q000378:metabolism; D010766:Phosphorylation; D013314:Stress, Mechanical; D013552:Swine; D017540:Tunica Media / Q000187:drug effects / Q000201:enzymology