Phorbol ester activation of the rat vascular myocyte Na(+)-H(+) exchanger isoform 1.
Vascular myocytes from the spontaneously hypertensive rat (SHR) demonstrate elevated Na(+)-H(+) exchanger activity associated with increased cell proliferation and hyperresponsiveness to agonists such as phorbol esters. Since the Na(+)-H(+) exchanger isoform 1 (NHE-1) is stimulated by protein kinase C, we have investigated the effects of phorbol esters on NHE-1 activity and its phosphorylation in vascular myocytes of these rats. SHR cells demonstrated a larger alkalinization response to 12-O-tetradecanoylphorbol 13-acetate than Wistar-Kyoto rat (WKY) cells. Kinetic analyses indicated that whereas 12-O-tetradecanoylphorbol 13-acetate increased the maximal transport capacity of NHE-1 in both cell types, affinity for H+ was increased in WKY cells and cooperativity for H+ at the internal modifier site was reduced in SHR cells. In neither cell type was the subcellular distribution of NHE-1 altered by phorbol ester stimulation. NHE-1 phosphorylation was markedly reduced in WKY cells stimulated by the phorbol ester, an effect abolished by inhibition of protein kinase C. In contrast, NHE-1 phosphorylation in quiescent SHR cells was approximately double that of WKY cells and was reduced after phorbol ester treatment. Inhibition of protein kinase C in SHR cells led to a marked elevation of NHE-1 phosphorylation that was not associated with a change in the exchanger activity, but WKY cells exhibited a small, insignificant rise in NHE-1 phosphorylation. Thus, the kinetic responses of NHE-1 to phorbol esters in vascular myocytes of these rat strains are different, the changes in exchanger kinetics of SHR resembling those described in human hypertension. NHE-1 phosphorylation has an inverse relationship with protein kinase C activity. However, modulation of NHE-1 phosphorylation may not be associated with concurrent alterations in activity, indicating a role for non-phosphorylation-dependent mechanisms.
Siczkowski
M
M
Department of Medicine and Therapeutics, Leicester (UK) Royal Infirmary.
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D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002478:Cells, Cultured; D006973:Hypertension / Q000378:metabolism*; D009131:Muscle, Smooth, Vascular / Q000378:metabolism*; D010703:Phorbol Esters / Q000494:pharmacology*; D010766:Phosphorylation / Q000187:drug effects; D051381:Rats; D011918:Rats, Inbred SHR; D011921:Rats, Inbred WKY; D017923:Sodium-Hydrogen Exchangers / Q000378:metabolism*
D010703:Phorbol Esters; D017923:Sodium-Hydrogen Exchangers