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


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.
Osanai
T
T
Second Department of Internal Medicine, Hirosaki University School of Medicine, Japan.
Kanazawa
T
T
Okuguchi
T
T
Kamada
T
T
Metoki
H
H
Oike
Y
Y
Onodera
K
K
D000818:Animals; D015153:Blotting, Western; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D002455:Cell Division / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D006096:Gramicidin / Q000494:pharmacology*; D006965:Hyperplasia; D006973:Hypertension / Q000378:metabolism*; D006984:Hypertrophy; D007476:Ionophores / Q000494:pharmacology*; D008297:Male; D024510:Muscle Development; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000187:drug effects / Q000254:growth & development*; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism; D051381:Rats; D011918:Rats, Inbred SHR; D011921:Rats, Inbred WKY; D012964:Sodium / Q000378:metabolism; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*; D013997:Time Factors
D007476:Ionophores; D006096:Gramicidin; D012964:Sodium; D011493:Protein Kinase C; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D013755:Tetradecanoylphorbol Acetate