Magnesium and the regulation of muscle contraction

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Magnesium and the regulation of muscle contraction!.2 JAMES D. POTIER, STEVEN P. ROBERTSON AND J. DAVID JOHNSON

, Section of Contractile Proteins, Department of Pharmacology and Cell Biophysics.

Uniumily o/Cincinnati College of Medicine, Cincinnati. Ohio 45267

The main purpose of this article iW review curre nt concepts on the dr M~+ plays in the Ca!l- regu laioJI of muscle contrac tion. The priaary consideration will be the effect yt has on the Cat+ binding proplI'Iies of the two general types of ~.affiniIY (EF ha nd-type) Cat+ IiKling sites, those thai are specific if Calf (Ca2+-specific reg ulatory1ffIe~tes). a nd those th a t !>ind Mg2+ OlIlIpetitiveJy (Ca H _Mg2+_type sites). ,~though this review will focus o n IlUscle Cat+ binding proteins, the p!l!ral principles e mphasized he re IiII apply to hig h -affinit y Call- bindilg prolcins found in other tissues. IROPONIN AND MUSCLE IGULATION


There a re a v" riety of Ca" binding site~ in muscle (e.g .. tro pon in. I)Uva lbumin. m yos in . and calmod ul in ) that may pla ya role in the regulation of mUKIe contractio n and ot he r enzymatic processes. Since most of th ese p ro teins also bind MgH. it is impo rtant to co nsider th e effect that the hi gh free Mg" concerllra ti on (mM) found in mu scle has on the ea" binding properties of th ese sites, T he majo r erreCl of Mg" is to greal l ~' reduce Ih e rale of ea" binding to the siles thaI bi nd Mg" and Ca" competiti vely (Cat+_Mg"_type sites found in tropo nin. pan·albumin, and m),,:>si n, which would be essentiall y saturated with Mg" in a relaxed muscle) due to the slow' dissociation of bound Mg" , Thus during a Ira nsie nt increase in lea" ) similar to tha t which ""ould occu r d u ri ng mu scle acti vat ion. th ese si tes ",'a uld bind very liHle Ca" a nd , co nsC(aill the d esirc:d tea"l; th e pH "~d~ .. dj uSoiefi when ne