[Effects of ANP upon ion pump activity and gene expression in aortic smooth muscle cells from spontaneously hypertensive rats].

Objective: To explore the effects of atrial natriuretic peptide (ANP) upon the activities of Na(+), K(+)-ATPase, Ca(2+)-ATPase and mRNA expression levels of Na(+), K(+)-ATPase alpha(1)-subunit and plasma membrane Ca(2+)-ATPase isoform 1 (PMCA1) in cultured thoracic aortic vascular smooth muscle cells (ASMCs) isolated from spontaneously hypertensive rats (SHR).

Methods: ASMCs isolated from 14-week-old male SHR and Wistar-Kyoto (WKY) rats were interference-cultured in different doses of ANP and Angiotensin II (AngII). The contents of ANP and AngII in supernatant from ASMCs were measured by radioimmunoassay. The activities of the above two ATPases were measured by biochemistry and enzymology. RT-PCR assay was employed to determine the relative levels of Na(+), K(+)-ATPase alpha(1)-subunit and PMCA1 mRNA in ASMCs.

Results: The ANP level of supernatant in SHR ASMCs was significantly lower than those from WKY control [(7.3 +/- 2.4) pg x 10(-6) cells vs (19.3 +/- 3.3) pg x 10(-6) cells, P < 0.01] while the content of AngII in SHR ASMCs was significantly higher than those from WKY control [(57 +/- 4) pg x 10(-6) cells vs (44 +/- 4) pg x 10(-6) cells, P < 0.01]. The activity of Na(+), K(+)-ATPase [(4.3 +/- 0.8) micromol x h(-1) x mg(-1) vs (5.3 +/- 1.0) micromol x h(-1) x mg(-1)], Ca(2+)-ATPase [(3.2 +/- 0.7) micromol x h(-1) x mg(-1) vs (4.5 +/- 0.7) micromol x h(-1) x mg(-1)] in ASMCs from SHR were significantly lower than those from WKY control (both P < 0.01). The mRNA expression of Na(+), K(+)-ATPase alpha(1)-subunit (0.524 +/- 0.025 vs 0.704 +/- 0.116), PMCA1 (0.193 +/- 0.030 vs 0.547 +/- 0.045) significantly decreased in ASMCs from SHR versus the WKY control (both P < 0.01). As compared with SHR control, exogenous ANP improved obviously the activities of Na(+), K(+)-ATPase, Ca(2+)-ATPase and expression of alpha(1)-subunit, PMCA1 mRNA in a does-dependent manner (P < 0.05-P < 0.01). Exogenous AngII (1 x 10(-9), 1 x 10(-8), 1 x 10(-7) mol/L) significantly repressed activities of Ca(2+)-ATPase and attenuated the expression of PMCA1 mRNA (P < 0.05-P < 0.01). Only AngII (1 x 10(-7) mol/L) significantly inhibited the activity of Na(+), K(+)-ATPase and attenuated the expression of Na(+), K(+)-ATPase alpha(1)-subunit mRNA (both P < 0.05). ANP antagonized the effects of AngII (1 x 10(-7) mol/L) upon the activities of two ATPases and the expression of Na(+), K(+)-ATPase alpha(1)-subunit PMCA1 mRNA (P < 0.05-P < 0.01). AngII (1 x 10(-7) mol/L) increased the Na(+), K(+)-ATPase activity and the expression of Na(+), K(+)-ATPase alpha(1)-subunit mRNA, repressed the Ca(2+)-ATPase activity and the expression of PMCA1 mRNA in ASMCs from WKY rat (P < 0.05-P < 0.01). ANP antagonized the effects of AngII (1 x 10(-7) mol/L) upon the activity of Ca(2+)-ATPase and the expression of PMCA1 mRNA (P < 0.05-P < 0.01), but did not antagonize the effects of AngII (1 x 10(-7) mol/L) upon the activity of Na(+), K(+)-ATPase and the expression of alpha(1)-subunit mRNA in ASMCs from WKY rats (P > 0.05).

Conclusion: The decreased activities of Na(+), K(+)-ATPase and Ca(2+)-ATPase may be related to the abnormal autocrine of ANP and AngII in ASMC of SHR. ANP can antagonize the effects of AngII upon the activities of two ATPases and the expression of Na(+), K(+)-ATPase alpha(1)-subunit PMCA1 mRNA.