MECHANISMS WHEREBY CYTOTOXIC T-LYMPHOCYTES DAMAGE GUINEA-PIG VENTRICULAR MYOCYTES IN-VITRO

We studied possible mechanisms whereby cytotoxic T lymphocytes (CTL) d amage the myocardium during the immunological rejection of the transpl anted heart, by investigating the in vitro interaction between CTL and cardiac myocytes. We utilized the patch-clamp technique to record mem brane currents and action potentials from concanavalin A-treated guine a-pig ventricular myocytes conjugated to mouse peritoneal exudate CTL (PEL). PEL-myocyte interaction reduced action potential duration at 50 % repolarization (APD(50)) from 731.7+/-57.8 to 195.3+/-58.0 ms, actio n potential amplitude from 134.9+/-1.9 to 104.2+/-6.2 mV and resting m embrane potential (V-m) from -80.9+/-0.5 to -72.5+/-1.5 mV. These chan ges were accompanied by generation of delayed afterdepolarizations, in dicative of intracellular [Ca2+] overload. The electrophysiological al terations were associated with myocyte shortening (within 28.9+/-2.8 m in) followed by complete cell destruction (within 43.5+/-4.3 min). To determine whether intracellular Ca2+ stores were involved in PEL-induc ed myocyte damage, the protective effects of ryanodine and caffeine we re investigated. While ryanodine (10 mu M) delayed the electrophysiolo gical and morphological alterations, caffeine (5 mM) provided signific ant protection, suggesting that Ca2+ release from intracellular stores contributes to PEL-induced damage to the myocytes. Based on our findi ngs, we suggest that the functional derangements seen in myocyte-lymph ocyte conjugates can contribute to the overall decline in cardiac func tion during heart transplant rejection.