Mechanisms whereby cytotoxic T lymphocytes damage guinea-pig ventricular myocytes in vitro

We studied possible mechanisms whereby cytotoxic T lymphocytes (CTL) damage the myocardium during the immunological rejection of the transplanted heart, by investigating the in vitro interaction between CTL and cardiac myocytes. We utilized the patch-clamp technique to record membrane currents and action potentials from concanavalin A-treated guinea-pig ventricular myocytes conjugated to mouse peritoneal exudate CTL (PEL). PEL-myocyte interaction reduced action potential duration at 50% repolarization (APD₅₀) from 731.7±57.8 to 195.3±58.0 ms, action potential amplitude from 134.9±1.9 to 104.2±6.2 mV and resting membrane potential (V_m) from –80.9±0.5 to –72.5±1.5 mV. These changes were accompanied by generation of delayed afterdepolarizations, indicative of intracellular Ca²⁺] overload. The electrophysiological alterations were associated with myocyte shortening (within 28.9±2.8 min) followed by complete cell destruction (within 43.5±4.3 min). To determine whether intracellular Ca²⁺ stores were involved in PEL-induced myocyte damage, the protective effects of ryanodine and caffeine were investigated. While ryanodine (10 M) delayed the electrophysiological and morphological alterations, caffeine (5 mM) provided significant protection, suggesting that Ca²⁺ release from intracellular stores contributes to PEL-induced damage to the myocytes. Based on our findings, we suggest that the functional derangements seen in myocyte-lymphocyte conjugates can contribute to the overall decline in cardiac function during heart transplant rejection.