EFFECTS OF ANISOSMOTIC STRESS ON CARDIAC-MUSCLE CELL LENGTH, DIAMETER, AREA, AND SARCOMERE-LENGTH

The purpose of this study was to examine the effects of anisosmotic st ress on adult mammalian cardiac muscle cell (cardiocyte) size. Cardioc yte size and sarcomere length were measured in cardiocytes isolated fr om 10 normal rats and 10 normal cats. Superfusate osmolarity was decre ased from 300 +/- 6 to 130 +/- 5 mosM and increased to 630 +/- 8 mosM. Cardiocyte size and sarcomere length increased progressively when osm olarity was decreased, and there were no significant differences betwe en cat and rat cardiocytes with respect to percent change in cardiocyt e area or diameter; however, there were significant differences in car diocyte length (2.8 +/- 0.3% in cat vs. 6.1 +/- 0.3% in rat, P < 0.05) and sarcomere length (3.3 +/- 0.3% in cat vs. 6.4 +/- 0.3% in rat, P < 0.05). To determine whether these species-dependent differences in l ength were related to diastolic interaction of the contractile element s or differences in relative passive stiffness, cardiocytes were subje cted to the osmolarity gradient 1) during treatment with 7 mM 2,3-buta nedione monoxime (BDM), which inhibits cross-bridge interaction, or 2) after pretreatment with 1 mM ethylene glycol-bis(beta-aminoethyl ethe r)-N,N,N',N'-tetraacetic acid (EGTA), a bivalent Ca2+ chelator. Treatm ent with EGTA or BDM abolished the differences between cat and rat car diocytes. Species-dependent differences therefore appeared to be relat ed to the degree of diastolic cross-bridge association and not differe nces in relative passive stiffness. In conclusion, the osmolarity vs. cell size relation is useful in assessing the cardiocyte response to a nisosmotic stress and may in future studies be useful in assessing cha nges in relative passive cardiocyte stiffness produced by pathological processes.