Sera from chronic chagasic patients depress cardiac electrogenesis and conduction

We report results obtained with sera from 58 chronic chagasic patients that were evaluated for effects on heart rate and atrioventricular (AV) conduct ion in isolated rabbit hearts and screened for the presence of muscarinic a nd beta-adrenergic activity. We show that sera from 26 patients decreased h eart rate, while 10 increased it and 22 had no effect. Additionally, sera f rom 20 of the 58 patients blocked AV conduction. Muscarinic activation seem s to be involved in both effects, but is not the only mechanism, since atro pine did not antagonize the decrease in heart rate in 23% of sera or AV blo ck in 40%. Sera from patients with complex arrhythmias were significantly m ore effective in depressing both heart rate and AV conduction. Sera that in duce increases in heart rate seem to operate exclusively through beta-adren ergic activation. Two of these sera, evaluated with respect to intercellula r communication in primary cultures of embryonic cardiomyocytes were able t o block gap junction conductance evaluated by a dye injection technique aft er 24-h exposure. The mechanisms underlying this uncoupling effect are curr ently being investigated.