Physiological changes induced in cardiac myocytes by cytotoxic T lymphocytes

The 'lethal hit' induced by viral specific, sensitized, cytotoxic T lymphocytes (CTL) attacking virus-infected heart cells is important in the pathogenesis of viral myocarditis and reflects the key role of CTL in this immune response. The mechanisms involved are incompletely understood. Studies of the physiological changes induced in mengovirus-infected, cultured, neonatal, rat heart cells by CTL that had been previously sensitized by the same virus are presented. The CTL were obtained from spleens of mengovirus-infected, major histocompatibility complex (MHC) matched adult rats. Cell wall motion was measured by an optical method, action potentials with intracellular microelectrodes, and total exchangeable calcium content by ⁴⁵Ca tracer measurements after loading the myocytes with ⁴⁵Ca and then exposing them to CTL. After 50 min (mean time) of exposing mengovirus-infected myocytes to the CTL, the mechanical relaxation of the myocyte was slowed, with a subsequent slowing of beating rate and a reduced amplitude of contraction. Impaired relaxation progressed, and prolonged oscillatory contractions lasting up to several seconds appeared, with accompanying oscillations in the prolonged plateau phase of the action potentials. Arrest of the myocyte contractions appeared 98 min (mean time) after exposure to CTL. These changes in action potentials and concentrations were reversible either by washout with the normal medium or by the addition of verapamil. The amount of total exchangeable calcium in the cultured myocytes, 1 h after exposure to CTL, was significantly increased. This increase was prevented by pretreatment with verapamil. It is concluded that infection of cultured myocytes with mengovirus predisposes them to attack by mengovirus specific CTL, and that persistent dysfunction of the myocyte is preceded by reversible changes in membrane potential and contraction. This is suggestive of an altered calcium handling by the myocytes possibly resulting in the cytotoxic effect.