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The responses of cardiac actomyosin to changes in the concentrations of Ca 2+ , Na + and K + were examined to evaluate the role that direct actions of these cations could play in the regulation of myocardial contractility. The sensitivity of the Mg 2+ -activated adenosine triphosphatase (ATPase) activity of reconstituted cardiac actomyosin to changing Ca 2+ concentration was similar to that for skeletal actomyosin although both cardiac myosin and actomyosin were less active than the corresponding skeletal proteins at all Ca 2+ concentrations. Activation of both myosins by either the cardiac or skeletal actintropomyosin complex was virtually absent when free Ca 2+ concentration was below 10 -7 M. Full activation was seen at Ca 2+ concentrations greater than 10 -5 M. These findings support the view that variations in intracellular Ca 2+ concentration play a role in regulating myocardial contractility. Replacement of KCl by NaCl stimulated both the ATPase activity and superprecipitation of cardiac actomyosin. The positive inotropic effects associated with replacement of intracellular K + by Na + , e.g. the positive staircase accompanying increased heart rate, may therefore be due, in part at least, to a direct action of Na + upon the contractile proteins.

The U.S. encompasses a heterogenous mix of people and health disparities exist for various subpopulations, such as minorities, women, people with limited English proficiency, those with low socioeconomic status, and other underserved groups. Differences in health outcomes arise in part due to inequalities and injustices rooted in biological, social, and structural factors. Because the origins of health disparities are multifactorial, the approaches to reduce, or even eliminate them, must be multifactorial as well. The social and behavioral sciences are well poised to address the myriad and complex factors that affect health outcomes, including those at the individual level (eg, individuals’ behaviors, attitudes, and beliefs), the neighborhood level (eg, housing), the community level (eg, cultural values and norms), and the policy level (eg, public policies that influence healthcare funding and access to healthcare resources and educational materials). In addition, the social and behavioral sciences (1) help equip government agencies with the perspectives and tools needed to promote health equity and (2) contribute to rigorous, evidence-based solutions for public health issues, such as disparities found in childhood vaccination rates, childhood obesity, tobacco use, and access to health information technology. The FDA, in particular, actively conducts social and behavioral sciences research to guide the Agency’s efforts to advance and support health equity.

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