Atrial natriuretic peptide (ANP) mediates a variety of physiological effects through its interaction with ANP-A, ANP-B or ANP-C receptors. However, controversies exist regarding the involvement of ANP-C receptor and adenylyl cyclase/cAMP signal-transduction systems to which these receptors are coupled in mediating these responses. In the present studies, we have employed an antisense approach to eliminate the ANP-C receptor and to examine the effect of this elimination on adenylyl cyclase inhibition. An 18-mer antisense phosphorothioate oligodeoxynucleotide (OH-2) targeted at the initiation codon of the ANP-C receptor was used to examine its effects on the expression of the ANP-C receptor and ANP-C-receptor-mediated inhibition of adenylyl cyclase in vascular smooth-muscle cells (A10). Treatment of the cells with antisense oligonucleotide resulted in complete attenuation of C-ANP4-23 [des(Gln18, Ser19, Gln20, Leu21, Gly22)ANP4-23-NH2]-mediated inhibition of adenylyl cyclase, whereas sense and missense oligomers did not affect the inhibition of adenylyl cyclase by C-ANP4-23. In addition, the stimulatory effects of guanine nucleotides, isoproterenol, sodium fluoride and forskolin as well as the inhibitory effects of angiotensin II on adenylyl cyclase were not affected by antisense-oligonucleotide treatment. The attenuation of C-ANP4-23-mediated inhibition of adenylyl cyclase by antisense oligonucleotide was dose- and time-dependent. A complete attenuation of ANP-C-receptor-mediated inhibition of adenylyl cyclase was observed at 2.5 μM. In addition, treatment of the cells with antisense oligonucleotide and not with sense or missense oligomers resulted in the inhibition of the levels of ANP-C-receptor protein and mRNA as determined by immunoblotting and Northern blotting using antisera against the ANP-C receptor and a cDNA probe of the ANP-C receptor respectively. On the other hand, ANP-A/B-receptor-mediated increases in cGMP levels were not inhibited by antisense-oligonucleotide treatment. Our results demonstrate conclusively that the elimination of ANP-C receptor by antisense oligonucleotide attenuates ANP-induced inhibition of adenylyl cyclase and provide evidence that antisense oligonucleotide of the ANP-C receptor may serve as a useful pharmacological tool to elucidate the physiological functions of the ANP-C receptor.

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