The human atrial trabecula: effects of calcium and temperature

The human atrial trabecular preparation is an in vitro model which has been used to evaluate drugs and conditions to which cardiac muscle is exposed perioperatively. During its development, modifications have been made to this preparation. Two important components affecting myocardial muscle contraction are temperature and calcium concentration of the muscle bath medium. Previously, these parameters were determined independently of one another and found to be 34 degrees C and 2.5 mM calcium in a minimal Tyrode's buffer with glucose. This study was undertaken to define the optimal temperature and calcium concentration which would result in the highest yield of muscles that satisfied rigorous criteria for acceptability: developed force (DF) greater than 0.8 g, resting force (RF) less than 0.7 g, cross-sectional area less than or equal to 1.0 mm2). A total of 134 trabeculae were tested using a modified Krebs-Henseleit buffer, enriched with Eagles' medium and containing either 1.25 or 2.5 mM calcium at 34 or 37 degrees C. The trabeculae contracting in 2.5 mM calcium at 37 degrees C resulted in the highest yield of 26% while those maintained at 34 degrees C in either 1.25 or 2.5 mM calcium led to 20 and 15% useful preparations respectively (P = N.S.). Trabeculae contracting at 37 degrees C in 1.25 mM calcium resulted in the poorest yield of 8% (P = 0.002). There is a small (5 to 7%), but significant (P = 0.02), decrease in DF in 1 h when all groups were analyzed together. The exclusion criteria which are applied eliminate variability due to disease and/or treatment, therefore only 20 to 25% are acceptable for study. In summary, with well-defined and stringently applied criteria, the human right atrial trabecular preparation can be a reliable and reproducible model functioning at 37 degrees C and 2.5 mM calcium for a variety of studies.