Specific inhibition of Na‐Ca exchange function by antisense oligodeoxynucleotides

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 (INaCa) 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 an INaCa 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 exchanger.