Cellular mechanism underlying LPS-induced inhibition of in vitro L-leucine transport across rabbit jejunum

Lipopolysaccharide (LPS) is a known causative agent of sepsis. In previous studies, we have shown that it reduces L-leucine mediated transport across the rabbit jejunum by about 30%. In this study, the mechanism(s) of LPS inhibition on amino acid transport were analysed in detail. LPS did not inhibit L-leucine transport across brush border membrane vesicles, suggesting the need for an intracellular step. The inhibitory effect of LPS was not altered by the addition of protein kinase A (PKA) inhibitor (IP(20), 10(-7) M) or an analog of cAMP (DB-cAMP, 3 x 10(-4) M), indicating that the PKA signal transduction pathway was not involved in the LPS effect. However, the inhibitory effect of LPS was suppressed by trifluoroperazine (10(-7) M), a Ca(2+)/calmodulin inhibitor and staurosporine (10(-7) M), an protein kinase C (PKC) inhibitor. Likewise, LPS inhibition disappeared in media without calcium. These results suggest that LPS could inhibit the intestinal uptake of L-leucine across the small intestine in vitro by intracellular processes related to calcium, involving PKC and calmodulin protein.