Cardiac performance in inbred rat genetic models of low and high running capacity

1. Previous work demonstrating that DA inbred rats are superior to COP inbr ed rats in aerobic treadmill running capacity has indicated their utility a s genetic models to explore this trait. We tested the general hypothesis th at intermediate phenotypes of cardiac function and calcium metabolism are r esponsible for the difference in capacity between these strains. 2. Logical cardiac trait differences were estimated at a tissue (isolated p apillary muscle), cellular (isolated left ventricular cells), and biochemic al level of organization. 3. DA hearts were found to give significantly higher values than COP hearts for: (1) maximal developed tension (38.3% greater), and rates of tension c hange in contraction (61%) or relaxation (59%) of isolated papillary muscle , (2) fractional shortening (50%), amplitude of the Ca2+ transient (78.6%), and caffeine-induced release of Ca2+ from the sarcoplasmic reticulum (SR; 260%) in isolated ventricular myocytes, and (3) Na+,K+-ATPase activity of i solated myocytes (17.3%). 4. Our results suggest that these trait differences may prove useful for fu rther studies into the genes responsible for natural variations in both ven tricular function and aerobic endurance capacity. Understanding the genetic basis of aerobic capacity will help define the continuum between health an d disease.