EFFECTS OF ALLOIMMUNE INJURY ON CONTRACTION AND RELAXATION IN CULTURED MYOCYTES AND INTACT CARDIAC ALLOGRAFTS

Objectives. This study was performed to determine the mechanisms by wh ich allosensitized lymphocytes cause contractile dysfunction in cultur ed ventricular myocytes and to compare the effects on isolated myocyte s with those observed in an intact heart preparation during allograft rejection. Background. Allograft rejection may be associated with reve rsible abnormalities of both systolic and diastolic function. The immu nologic mechanisms that cause ventricular dysfunction are poorly under stood. Methods. Vascularized heterotopic abdominal heart transplantati on,vas performed in mice. Contractile function of excised allografts u ndergoing rejection was assessed using a Langendorff perfusion apparat us and a strain gauge. Spontaneously beating monolayers of cultured ve ntricular myocytes from donor strain fetal mice were exposed to the al losensitized cytotoxic T lymphocytes, and the effects on myocyte motio n, intracellular calcium transients, relaxation half-time, membrane po tential and myocyte lysis (chromium-51 release) were measured. Results . In intact hearts, histologically mild rejection without myocyte necr osis was associated with decreased systolic function without slowing o f relaxation. In cultured fetal myocytes, sensitized lymphocytes induc ed a progressive decrease in the amplitudes of myocyte motion and calc ium transients, with cessation of beating within 40 min. Also, the dia stolic membrane potential and amplitude of the action potential decrea sed. Relaxation half-time, as estimated by measurement of cell motion, was unchanged. The effect,vas allospecific and was reversible with ea rly removal of lymphocytes from the myocyte monolayer. Pretreatment of lymphocytes with the degranulation inhibitor 4,4'-diisothiocyano- 2,2 '-disulfonic acid stilbene blocked both the negative inotropic effect and myocyte lysis. Conclusions. We conclude that impaired relaxation i s not a prominent feature of contractile dysfunction caused directly i n myocytes by alloimmune injury from cytotoxic lymphocytes. Allosensit ized lymphocytes can cause reversible systolic dysfunction in myocytes by means of a direct cell-cell interaction. This effect may be in par t responsible for the reversible systolic dysfunction associated with allograft rejection.