Lipopolysaccharide induces cell shrinkage in rabbit ventricular cardiac myocytes

The effects of 10 ng/ml of lipopolysaccharide (LPS) on cell volume were examined in rabbit left ventricular myocytes. The myocytes were isolated with depyrogenated digestive enzymes (<0.7 ng/ml of LPS) to minimize tolerance. Myocyte cross-sectional area (CSA) did not change after 1 h of LPS. However after 8 h, the CSA decreased to 0.93 ± 0.01 (SE) of the baseline CSA (time = 0) in 19 LPS-exposed myocytes compared with 1.00 ± 0.01 in 13 control myocytes (P = 0.0015). LPS-induced cell shrinkage was completely blocked by coincubation with 1 mM N-mono-methyl-L-arginine, indicating a nitric oxide- mediated mechanism. Cardiac guanosine 3',5'-cyclic monophosphate (cGMP) did not change after 1 h but increased 6 h after LPS (548 ± 31 vs. 312 ± 20 fmol/mg protein in control cells; P < 0.05). After 8 h, bumetanide (10 μM for 30 min), a Na⁺/K⁺/2Cl^- cotransport inhibitor, decreased the CSA in 15 control myocytes to 0.92 ± 0.02 of the baseline CSA. However, in 19 myocytes with a CSA of 0.93 ± 0.01 of baseline after 8 h of LPS, the addition of bumetanide caused no additional cell shrinkage. We conclude that low levels of LPS increase cardiac cGMP to inhibit Na⁺/K⁺/2Cl^- cotransport, causing significant cell shrinkage in cardiac myocytes.