The goal of the present study was to evaluate the effects of Ang II on the current produced by the Na<SUP>+</SUP>-Ca<SUP>2+</SUP> exchanger (I<SUB>NCX</SUB>) working in the reverse mode and the possible autocrine role played by the release of endothelin (ET) in these actions. I<SUB>NCX</SUB> was studied in isolation in cat cardiac myocytes. Angiotensin II (Ang II) (100 nmol/L) increased I<SUB>NCX</SUB> at potentials higher than 0 mV (at +60 mV: 2.07±0.22 pA/pF in control versus 2.73±0.22 pA/pF in Ang II, n = 9; P < 0.05). The increase in I<SUB>NCX</SUB> induced by Ang II was prevented by the treatment of the cells with the unspecific blocker of the ET receptors, TAK 044 (1 μmol/L) (at +60 mV: 2.15±0.27 pA/pF in control versus 2.01±0.26 pA/pF in Ang II, n=5, NS). These results show, for the first time, that the effect of Ang II on I<SUB>NCX</SUB> is the result of the autocrine actions of ET released by the octapeptide.Facultad de Ciencias MédicasCentro de Investigaciones Cardiovasculares