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 activities 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.