Shock/Sepsis/Trauma/Critical CareLipopolysaccharide and cytokines inhibit rat cardiomyocyte contractility in vitro

BackgroundSepsis-induced cardiomyopathy (SIC) is thought to be the result of detrimental effects of inflammatory mediators on the cardiac muscle. Here we studied the effects of prolonged (24 ± 4 h) exposure of adult rat ventricular myocytes (ARVM) to bacterial lipopolysaccharide (LPS) and inflammatory cytokines tumor necrosis factor (TNF) and interleukins-1 (IL-1) and IL-6.Materials and methodsWe measured sarcomere shortening (SS) and cellular calcium (Ca2+) transients (ΔCai, with fura-2 AM) in isolated cardiomyocytes externally paced at 5 Hz at 37°C.ResultsSS decreased after incubation with LPS (100 μg/mL), IL-1 (100 ng/mL), and IL-6 (30 ng/mL), but not with lesser doses of these mediators, or TNF (10-100 ng/mL). A combination of LPS (100 μg/mL), TNF, IL-1, and IL-6 (each 100 ng/mL; i.e., “Cytomix-100”) induced a maximal decrease in SS and ΔCai. Sarcoplasmic reticulum (SR) Ca2+ load (CaSR, measured with caffeine) was unchanged by Cytomix-100; however, SR fractional release (ΔCai/CaSR) was decreased. Underlying these effects, Ca2+ influx into the cell (via L-type Ca2+ channels, LTCC) and Ca2+ extrusion via Na+/Ca2+ exchange were decreased by Cytomix-100. SR Ca2+ pump (SERCA) (SR Ca2+ ATPase) was not affected.ConclusionsProlonged exposure of ARVM to a mixture of LPS and inflammatory cytokines inhibits cell contractility. The effect is mediated by the inhibition of Ca2+ influx via LTCC, and partially opposed by the inhibition of Na+/Ca2+ exchange. Because both mechanisms are commonly seen in animal models of SIC, we conclude that prolonged challenge with Cytomix-100 of ARVM may represent an accurate in vitro model for SIC.