Whole-cell currents from the cloned canine cardiac Na+/Ca2+ exchanger NCX1 overexpressed in a fibroblast cell CCL39

 A conventional patch-clamp technique was used to record the whole-cell current from the cloned canine cardiac Na⁺/Ca²⁺ exchanger NCX1 overexpressed in a fibroblast cell. Ca²⁺ was extracellularly applied to the Na⁺-loaded cell to activate the outward current by operating the reverse mode of NCX1. No measurable outward current was ever elicited from the nontransfected cell. Na⁺/Ca²⁺ exchange blocker 5 mM Ni²⁺ or 3 μM KB-R7943 that was applied extracellularly abolished the outward current. With 140 mM external Li⁺ (replacing Na⁺), the outward current was transient during the Ca²⁺ application. In contrast, with 140 mM external Na⁺, the outward current was maintained without any inactivation during the Ca²⁺ application. I–V relations predicted from the whole-cell clamp protocols used were obtained both before and during the Ca²⁺ application. The exchanger whole-cell currents are thus successfully detectable from NCX1 which is overexpressed in this stable transfectant system. Received: 28 February 1997 / Accepted: 9 April 1997