INTERLEUKIN-6 INHIBITS HEPATOCYTE TAUROCHOLATE UPTAKE AND SODIUM-POTASSIUM-ADENOSINE-TRIPHOSPHATASE ACTIVITY

The potential effects of cytokines on hepatocellular transport functions remain undefined. Interleukin-g (IL-6) is a cytokine that is produced in sepsis, hepatitis, and other inflammatory conditions often associated with cholestasis. Using cultured rat hepatocytes, we have investigated the effects of IL-6 on hepatocellular bile salt uptake. Because hepatocyte Na+-K+-adenosinetriphosphatase (ATPase) produces the electrochemical gradient that drives sodium-dependent bile salt cotransport, we also examined the effects of IL-6 on Na+-K+-ATPase activity. Hepatocytes cultured for 20 h in media containing IL-6 exhibited a dose-dependent noncompetitive inhibition of [H-3]taurocholate uptake, which was maximal at an IL-6 dose of: 100 U/ml. IL-6 treatment had no effect on hepatocyte sodium-independent taurocholate uptake. Northern blotting of RNA from cultured hepatocytes revealed that IL-6 had no effect on steady-state RNA levels of the Na+-taurocholate transporter (Ntcp). Hepatocytes incubated with IL-6 for 20 h, however, exhibited a 55% decrease in hepatocyte Na+-K+-ATPase activity. This effect also was dose dependent, with maximal inhibition occurring at an IL-6 dose of 100 U/ml. Similar treatment with IL-6 did not influence hepatocyte Mg2+-ATPase activity. The inhibition of Na+-K+-ATPase activity induced by IL-6 provides a putative mechanism for the observed inhibition of sodium-dependent taurocholate uptake. Since modulation of bile salt transport and Na+-K+-ATPase activity occurred at IL-6 concentrations comparable to the serum levels observed in patients with severe inflammatory states, these findings have potential pathophysiological relevance for the cholestasis of sepsis and other inflammatory disorders.