Millman, Barry M. The Filament Lattice of Striated Muscle. Physiol. Rev. 78: 359–391, 1998. — The filament lattice of striated muscle is an overlapping hexagonal array of thick and thin filaments w...

The Filament Lattice of Striated Muscle

Summary


1. To celebrate this Festschrift for Professor Colin Gibbs, as an invited speaker, I would like to review briefly my 35 year research career in cardiac physiology.



2. My career started in the late 1960s in Tokyo with my serendipitous discovery of Emax (ventricular end-systolic maximum elastance) as a load-independent contractility index based on the time-varying elastance (E(t)) model of the ventricle. Professor K Sagawa at the Johns Hopkins University, USA, whom I joined in 1971, encouraged me to go further.



3. The next serendipitous event in my career was the discovery of ventricular pressure–volume area (PVA) as a measure of total mechanical energy of ventricular contraction in the late 1970s. The PVA concept was theoretically deducible from the E(t) and Emax concept and correlated surprisingly well with ventricular O2 consumption (Vo2).



4. Professor Gibbs' intuitive recognition of the significance of PVA in myocardial energetics in the 1980–1990s greatly encouraged me thereafter. The third serendipitous event in my career occurred in the mid 1990s and was my discovery of a novel integrative analysis method to assess the total amount of Ca2+ recruited in each excitation–contraction coupling from the decay rate of postextrasystolic potentiation, taking advantage of the Emax–PVA–Vo2 framework.



5. I am now hoping to experience one more serendipitous experience by developing an integrative analysis method of cross-bridge cycling in a beating heart using the Emax and PVA concepts.

https://onlinelibrary.wiley.com/doi/pdf/10.1046/j.1440-1681.2003.03879.x

Cardiac Energetics: From Emax to Pressure-Volume Area

Synchrotron radiation (SR) is increasingly being used for micro-level and nano-level functional imaging in in vivo animal experiments This review focuses on the methodology that enables repeated and regional assessment of vessel internal diameter and flow in the resistance vessels of different organ systems In particular, SR absorption microangiography approaches offer unique opportunities for real-time in vivo vascular imaging in small animals, even during dynamic motion of the heart and lungs We also describe recent progress in the translation of multiple phase-contrast imaging techniques from ex vivo to in vivo small-animal studies Furthermore, we also review the utility of SR for multiple pinpoint (dimensions 02×02 mm) assessments of myocardial function at the cross-bridge level in different regions of the heart using small-angle X-ray scattering, resulting from increases in SR flux at modern facilities Finally, we present cases for the use of complementary SR approaches to study cardiovascular function, particularly the pathological changes associated with disease using small-animal models

Synchrotron radiation imaging for advancing our understanding of cardiovascular function

1. By applying the X-ray diffraction method to chemically skinned papillary muscles of the rat, the transfer of myosin heads from the thick to the thin filaments was studied as a function of Ca2+ concentration. 2. No significant transfer of the heads occurred when the Ca2+ concentration was below the threshold of contraction (pCa 6.2). 3. During the maximum isometric contraction at pCa 4.4, 80% of the myosin heads were transferred to the thin filament. 4. When the muscle was activated isometrically at low Ca2+ concentrations (pCa 6.2-5.8), where the average tension was less than 20% of the maximum, a disproportionately large number of myosin heads were transferred to the thin filament. 5. It was concluded that a significant fraction of the heads transferred at the low Ca2+ concentrations does not produce tension.

Cross-bridge movement in rat cardiac muscle as a function of calcium concentration

Global cardiac function: mechano-energetico-informatics

1. The equatorial X-ray diffraction pattern was recorded from a papillary muscle of a cross-circulated canine heart at different phases of the cardiac cycle. The intensity ratio of the 1, 0 and the 1, 1 reflexions (I1, o/I1,1) was 0-79 in the systolic phase and 1-19 in the diastolic phase. 2. Using the intensity ratio obtained, the approximate proportion of the myosin projections present in the vicinity of the thin filaments was calculated. This was 70-71% in the systolic phase and 51-52% in the diastolic phase of the total myosin projections. 3. The peak systolic tension was roughly proportional to the proportion of the projections present in the vicinity of the thin filaments during systole. 4. The projections which stayed in the vicinity of the thin filaments during diastole did not produce significant contractile force.

I Matsubara

Papers

An X‐ray diffraction study of the cross‐circulated canine heart.