Calcium regulation of cardiac myofibrillar activation: Effects of MgATP

✍ Scribed by Solaro, R. John

• Book ID: 102438413
• Publisher: Wiley (John Wiley & Sons)
• Year: 1975
• Tongue: English
• Weight: 398 KB
• Volume: 3
• Category: Article
• ISSN: 0091-7419
• DOI: 10.1002/jss.400030409

✦ Synopsis

Abstract

In 2 mM MgATP, 0.08 ionic strength and 1 mM free Mg^++^ cardiac myofibrils bound 3.5 nmoles Ca/mg protein at maximal ATPase activation. Significant amounts of Ca were also bound to cardiac myosin with these same conditions. By subtraction of this myosin‐bound Ca we obtained an estimate of 4 moles Ca bound per mole of myofibrillar troponin at maximal ATPase. We found, however, that Ca activation of myofibrillar ATPase could be estimated assuming that only two of troponin's Ca‐binding sites are engaged in regulation of crossbridge activity. Increase in MgATP from 0.3 to 5.0 mM raised the free Ca, giving half‐maximal isometric tension or ATPase. Although part of this shift is most probably due to changes in the number of rigor (nucleotidefree) actin‐myosin linkages, the rightward shift of the free Ca^++^‐activation relation with increase in MgATP from 2 to 5 mM appears to be due to effects of active (nucleotide‐containing) actin‐myosin linkages.