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 which allosensitized lymphocytes cause contractile dysfunction in cultured ventricular myocytes and to compare the effects on isolated myocytes with those observed in an intact heart preparation during allograft rejection. Background. Allograft rejection may be associated with reversible abnormalities of both systolic and diastolic function. The immunologic mechanisms that cause ventricular dysfunction are poorly understood. Methods. Vascularized heterotopic abdominal heart transplantation,vas performed in mice. Contractile function of excised allografts undergoing rejection was assessed using a Langendorff perfusion apparatus and a strain gauge. Spontaneously beating monolayers of cultured ventricular myocytes from donor strain fetal mice were exposed to the allosensitized cytotoxic T lymphocytes, and the effects on myocyte motion, intracellular calcium transients, relaxation half-time, membrane potential and myocyte lysis (chromium-51 release) were measured. Results. In intact hearts, histologically mild rejection without myocyte necrosis was associated with decreased systolic function without slowing of relaxation. In cultured fetal myocytes, sensitized lymphocytes induced a progressive decrease in the amplitudes of myocyte motion and calcium transients, with cessation of beating within 40 min. Also, the diastolic membrane potential and amplitude of the action potential decreased. Relaxation half-time, as estimated by measurement of cell motion, was unchanged. The effect,vas allospecific and was reversible with early 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 is not a prominent feature of contractile dysfunction caused directly in myocytes by alloimmune injury from cytotoxic lymphocytes. Allosensitized lymphocytes can cause reversible systolic dysfunction in myocytes by means of a direct cell-cell interaction. This effect may be in part responsible for the reversible systolic dysfunction associated with allograft rejection.