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Cardiovascular Research 1996 31(1):124-131; doi:10.1016/S0008-6363(95)00193-X
© 1996 by European Society of Cardiology
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Copyright © 1996, European Society of Cardiology

Sodium ionophore converts growth manner of vascular smooth muscle cells from spontaneously hypertensive rats

Tomohiro Osanai*,a, Takemichi Kanazawaa, Tomoyuki Okuguchia, Takaatsu Kamadaa, Hirobumi Metokib, Yasaburo Oikeb and Kogo Onoderaa

aSecond Department of Internal medicine, Hirosaki University School of Medicine, 5-zaifu-cho, Hirosaki 036, Japan
bReimeikyo Rehabilitation Hospital, ikarigaseki-mura, Minami tsugarugun, Aomori Pref. 038-01, Japan

* Corresponding author. Tel. (+81-172) 33-5111; Fax (+81-172) 35-9190.

Objectives: Vasoconstrictor peptides such as endothelin (ET) cause hypertrophy of vascular smooth muscle cells (VSMC) in Wistar Kyoto rats (WKY) and hyperplasia in spontaneously hypertensive rats (SHR). They also induce an increase in Na+ concentration ([Na+]i) and activate protein kinase C (PKC) independently. Therefore, we tested the hypothesis that the increase in [Na+]i may be involved in the conversion of growth manner under activated PKC in SHR VSMC. Methods and Results: 10–7 M phorbol ester (TPA) increased the diameter and protein content of VSMC from both strains under 18% serum conditions. Further addition of 10–6 M gramicidin (Na+ ionophore) converted TPA-induced hypertrophy to hyperplasia, which was due to the quick transition from S to G2/M phase, only in SHR VSMC. Western blot analysis showed that serum- and TPA-induced tyrosine phosphorylation of mitogen-activated protein (MAP) kinase was potentiated by 10–6 M gramicidin in SHR. [Na+]i, which was measured by sodium-binding benzofuran isophthalate (SBFI), was increased about 35 mM by 10–6 M gramicidin in both strains, but TPA did not affect basal [Na+]i and the gramicidin-induced increase in [Na+]i. Conclusions: We conclude that sodium ionophore may convert hypertrophy to hyperplasia synergistically with activated PKC in SHR VSMC, possibly by MAP kinase phosphorylation.

KEYWORDS Rat, spontaneously hypertensive; MAP-kinase; Hypertrophy; Hyperplasia; Vascular smooth muscle; Gramicidin; Phorbol ester


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