| Abstract: | Bordetella pertussis, the pathogen responsible for whooping cough, releases a soluble calmodulin-sensitive adenylate cyclase into its culture medium which enters several different types of animal cells and elevates intracellular cAMP. In this study, the influence of B. pertussis adenylate cyclase on intracellular cAMP levels of cultured chick cardiac cells and the beating rates of chick cardiac cell aggregates was examined. Treatment with B. pertussis adenylate cyclase caused up to a 60-fold increase in intracellular cAMP which was significantly greater than that caused by forskolin or isoproterenol. Increases in intracellular cAMP caused by B. pertussis adenylate cyclase were observed within 2 min after treating cells with the enzyme, and binding of calmodulin to the enzyme inhibited these effects. In addition, high concentrations of the enzyme completely inhibited the beating of cardiac cells. However, lower concentrations of the adenylate cyclase accelerated beating rates 30-40% and cardiac cells continued to beat at an accelerated rate for at least 30 min. These data indicate that B. pertussis adenylate cyclase invades chick cardiac cells and catalyzes significant increases in intracellular cAMP. It is proposed that the effect of the enzyme on the beating rates of heart cell aggregates may be due to alteration of intracellular cAMP levels. |
