• Endothelin-1;
  • KB-R7943 (2-[2-[4-(4-nitrobenzyloxy)phenyl]ethyl]isothiourea methanesulphonate);
  • cell contraction;
  • Ca2+ transient;
  • Na+/Ca2+ exchanger;
  • adult rabbit ventricular cardiac myocytes
  • The effects of endothelin-1 (ET-1) on intracellular Ca2+ ion level and cell contraction were simultaneously investigated in rabbit ventricular cardiac myocytes loaded with indo-1/AM. The role of Na+/Ca2+ exchange in ET-1-induced positive inotropic effect (PIE) was examined by using KB-R7943 (2-[2-[4-(4-nitrobenzyloxy)phenyl]ethyl]isothiourea methanesulphonate), a selective inhibitor of reverse mode Na+/Ca2+ exchange.

  • ET-1 at 0.3 pM–1 nM increased cell contraction and Ca2+ transient (CaT) with EC50 values of 2.9 pM and 1.2 pM, respectively, and the increase in amplitude of CaT was much smaller relative to the PIE: ET-1 at 1 nM increased peak cell shortening by 237%, while it increased peak CaT by 167%. For a given level of PIE, ET-1-induced increase in CaT was much smaller than that induced by elevation of [Ca2+]o and by isoprenaline. Therefore, ET-1 shifted the relationship between peak CaT and cell shortening to the left relative to the relationship for increase in [Ca2+]o, an indication that ET-1 increased myofibrillar Ca2+ sensitivity.

  • KB-R7943 at 0.1 μM and higher inhibited contraction and CaT induced by 0.1 nM ET-1 and at 0.3 μM it abolished the increase in CaT while inhibiting the PIE by 48.1%. Over concentration range of 0.1–0.3 μM, KB-R7943 neither inhibited baseline contraction and CaT nor the isoprenaline-induced response, although at 1 μM and higher it had a significant inhibitory action on these responses.

  • These results indicate that in rabbit ventricular myocytes both increases in CaT and myofibrillar Ca2+ sensitivity contribute to the ET-induced PIE, and the activation of reverse mode Na+/Ca2+ exchange may play a crucial role in increase in CaT induced by ET-1 in rabbit ventricular cardiac myocytes.

British Journal of Pharmacology (1999) 126, 1785–1795; doi:10.1038/sj.bjp.0702454