Mechanism of Action of Bordetella Heat-Labile Toxin on Vascular Smooth Muscle Strips and Cells(I. Characterization of Virulence Factors of Bordetella pertussis)(Current Studies on Future Vaccines)

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The mechanism of action of Bordetella heat-labile toxin (HLT) was analyzed in vitro using vascular smooth muscle strips (VSMS) and cultured cells (VSMC), from aortas of pig, guinea pig, rabbit, rat or mouse. HLT induced contractions to both VSMS and VSMC, but not other types of tissues and cells. HLT induced the increase of Ca^<2+>-influx in parallel with the contraction. These HLT activities were not influenced by the addition of verapamil, diltiazem, or TMB-8, though a certain extension of the lag period was seen. The contractile action on VSMC was not influenced by a various blockers of cascades or systems. The HLT-induced contraction in VSMC was completely inhibited by H-7, but not by H-8. HLT did not induce specific activation of the protein kinases in VSMC. HLT induced the permeability changes in VSMS or VSMC membranes to cyclic nucleotides or trypan blue. Both HLT-induced contraction and permeability change were inhibited by dextran of M. W. 8,000. ^<125>I-HLT bound immediately to VSMC depending on the HLT dose. At 37℃, the binding ratio in maximum was approximately 0.8% of total HLT added at 60 min after exposure. At 4℃, it was less than 20% of that at 37℃. The labeled HLT binding to VSMC was released readily by washing. From these results, possible mechanism of HLT action was discussed.
1988-09-22