PHYSIOLOGICAL-EFFECTS OF NA+ CA2+ EXCHANGER KNOCKDOWN BY ANTISENSE OLIGODEOXYNUCLEOTIDES IN ARTERIAL MYOCYTES/

Antisense oligodeoxynucleotides (AS-oligos) targeted to the Na+/Ca2+ e xchanger (NCX) inhibit NCX-mediated Ca2+ influx in mesenteric artery ( MA) myocytes [Am. J. Physiol. 269 (Cell Physiol. 38): C1340-C1345, 199 5]. Here, we show AS-oligo knockdown of NCX-mediated Ca2+ efflux. In i nitial experiments, the cytosolic free Ca2+ concentration ([Ca2+](cyt) ) was raised, and sarcoplasmic reticulum (SR) Ca2+ sequestration was b locked with caffeine and cyclopiazonic acid; the extracellular Na+-dep endent (NCX) component of Ca2+ efflux was then selectively inhibited i n AS-oligo-treated cells but not in controls (no oligos or nonsense ol igos). In contrast, the La3+-sensitive (plasmalemma Ca2+ pump) compone nt of Ca2+ efflux was unaffected in AS-oligo-treated cells. Knockdown of NCX activity was reversed by incubating AS-oligo-treated cells in n ormal media for 5 days. Transient [Ca2+](cyt) elevations evoked by ser otonin (5-HT) at 15-min intervals in AS-oligo-treated cells were indis tinguishable from those in controls. When cells were stimulated every 3 min, however, the peak amplitudes of the second and third responses were larger, and [Ca2+](cyst) returned to baseline more slowly, in AS- oligo-treated cells than in controls. Peak 5-HT-evoked responses in th e controls, but not AS-oligo-treated cells, were augmented more than t wofold in Na+-free media. This implies that NCX is involved in Na+ gra dient modulation of SR Ca2+ stores and cell responsiveness. The repeti tive stimulation data suggest that the NCX may be important during ton ic activation of arterial myocytes.