ELECTROGENIC SODIUM-CALCIUM EXCHANGE AND CARDIAC CELLULAR ELECTRICAL-ACTIVITY

Several studies have shown that the Na-Ca exchange is electrogenic in cardiac tissues and that the current carried by the exchange, iNa-Ca, participates in the development of the cardiac action potential platea u. The aim of the present study was to assess the contribution of iNa- Ca to the development of the plateau in different preparations i.e. no rmal and hypertrophied (DOCA-salt) perfused mt hearts, normal ann dila ted (MS 200 strain) perfused hamster hearts and normal human atrial my ocytes and to examine the repercussion of iNa-Ca suppression on the gl obal electrogram of the perfused guinea-pig heart. iNa-Ca,vcrs suppres sed by briefly substituting lithium for sodium (Li test). In the norma l rat heart, the Li test resulted in a depression of the late componen t of the plateau. In the severely hypertrophied rat heart, the action potential was lenghtened, the two components of the plateau barely dis tinguishable The part of the plateau suppressed during Li perfusion tr ;as not larger in amplitude than in the normal rat heart, but was of m uch longer duration. in the dilated heart of hamsters older. than 60 d ays of age the shortening effect of the Li test was much larger than i n the normal hamster hemt indicating a strongly increased contribution of iNa-Ca to the plateau development during dilatation. The contribut ion of iNa-Ca to the action potential plateau of human atrial myocytes was as large that folded in animal ventricles and varied with the typ e of cell studied In the perfused guinea-pig heart the Li test resulte d in a sizeable shortening of PT duration and a marked decrease in T w ave amplitude suggesting that iNa-Cu may be a major source of current in the building up of the ventricular complex of the electrocardiogram in normal and pathological conditions.