Lectin-induced increase in microvascular permeability to colloidal carbon in vitro may involve protein kinase C activation.

Two plant lectins, wheat germ agglutinin (WGA) and concanavalin A (Con A), which are known to bind to endothelial cells (ECs), were found to increase the leakage of colloidal carbon (CC) into the walls of microvessels in the villi of rat small intestine, when added to a gelatin-containing perfusate (GPSS) at a concentration of 10 micrograms/ml. Pretreatment of the microvessels with the protein kinase C (PKC) inhibitor Ro 31-8220 (1 x 10(-6) M) significantly reduced this effect. In contrast, the leakage of CC in response to A23187 (1 x 10(-4) M) was not affected by Ro 31-8220. Peanut agglutinin (PNA) and succinyl concanavalin A (SuccCon A), which do not bind to ECs, had no effect at a concentration of 10 micrograms/ml. A lower concentration of WGA (1 microgram/ml) had no significant effect of its own, but significantly reduced the leakage of CC in response to both platelet-activating factor (PAF, 5 x 10(-6) M) and 5-hydroxytryptamine (5-HT, 1 x 10(-4) M), but not to beta-phorbol 12,13-dibutyrate (PDB, 1 x 10(-6) M). These results suggest that all these effects of WGA and Con A involve cell surface receptors, albeit in a non-specific way. A possible mode of action is discussed.