Specific inhibition of Na‐Ca exchange function by antisense oligodeoxynucleotides

Abstract

The Na‐Ca exchanger is essential for the Ca²⁺ homeostasis in many cell types. This transporter has been difficult to investigate because no specific inhibitor is available. We have synthesized an antisense oligodeoxynucleotide directed against the rat cardiac Na‐Ca exchanger mRNA. To estimate the activity of the Na‐Ca exchange in single cultured myocytes, the exchange current (I _NaCa) was measured with the voltage‐clamp technique while the intracellular Ca²⁺ concentration ([Ca²⁺ _i]) was simultaneously recorded. Most cells exposed to antisense oligodeoxynucleotide showed neither anI _NaCa nor an increase of [Ca²⁺]_i upon extracellular Na⁺ removal. Liberation of Ca²⁺ by flashphotolysis of caged Ca²⁺ was not followed by a decay of [Ca²⁺]_i in cells exposed to the antisense oligonucleotide, whereas in control cells resting [Ca²⁺]_i was reached 6 s after the flash. Control experiments with non‐sense and mismatched oligonucleotides were performed to exclude unspecific inhibitory effects. These results demonstrate that the Na‐Ca exchange was specifically and completely suppressed and that antisense oligodeoxynucleotides represent a useful tool to investigate the cellular and molecular properties of the Na‐Ca exhanger.