Infection of L6E9 myoblasts with Trypanosoma cruzi alters adenylate cyclase activity and guanine nucleotide binding proteins

We studied the consequences of infection of L6E9 myoblasts with T. cruzi on the adenylate cyclase complex to test the hypothesis that infection alters the functional properties of the guanine nucleotide regulatory proteins, Ns and Ni. Stimulating activities of adenylate cyclase due to isoproterenol, isoproterenol plus Gpp(NH)p, or forskolin (activities mediated by Ns) are not altered by infection. However, inhibitory activites mediated by Ni [Gpp(NH)p, acetylcholine, and adenosine inhibition of forskolin‐dependent adenylate cyclase activity] are compromised by infection. The reduction in adenosine's inhibition of forskolin‐dependent adenylate cyclase activity is seen throughout the effective concentration range of adenosine. Pertussis toxin does not change basal or stimulated adenylate cyclase activity in infected cells compared with normal uninfected cells, nor does it alter the inhibiting action of adenosine. To evaluate the coupling proteins (Ns and Ni) involved in the stimulation and inhibition of adenylate cyclase more directly, cholera‐ and pertussis‐toxin‐dependent ADP ribosylation studies were performed. The incorporation of [³²P]ADP ribose in the presence (specific) or absence (nonspecific) of the toxins was markedly decreased in membranes prepared from infected cells. However, in membranes prepared from infected or uninfected cells previously treated with pertussis toxin, there was a significant reduction in specific pertussis‐toxin‐dependent ADP ribosylation. The infection‐associated diminution in toxin‐dependent ADP ribosylation complements the impaired inhibition of adenylate cyclase data. Collectively, the data further substantiate an infection‐associated alteration in the adenylate cyclase complex, probably at the level of the guanine nucleotide binding proteins.