Urotensin II activates sarcolemmal Na+/H+ exchanger in adult rat ventricular myocytes.
OBJECTIVE
Our aims in the present study were (1) to determine the effects of urotensin II (UT-II) on the sarcolemmal Na/H exchanger (NHE1) activity, and (2) to investigate possible kinase pathways for UT-II-mediated NHE1 stimulation.


METHODS
In single rat ventricular myocytes (n = 5-10/group) loaded with the pH-sensitive fluoroprobe carboxy-seminaphthorhodafluor-1, acid efflux rates (JH) were determined as an index of NHE1 activity by rate of recovery of intracellular pH (pHi) from NH4Cl-induced acidosis and the intrinsic buffering power. Phosphorylation of extracellular signal-regulated kinase (ERK), a key kinase of NHE1 activation, was determined by Western blot analysis.


RESULTS
JH increased by 31%-71% relative to control in the presence of 100 nmol/L UT-II at pHi range of 6.6-7.0. Stimulation of NHE1 activity by UT-II was abolished by inhibitors of phospholipase C, protein kinase C, and ERK kinase; 2-nitro-4-carboxyphenil-N,N-diphenilcarbamate at 100 micromol/L, GF109203X at 300 nmol/L, and PD98059 at 50 micromol/L, respectively. Moreover, UT-II at 100 nmol/L produced a significant increase in cellular ERK1/2 phosphorylation, which was also inhibited by those inhibitors.


CONCLUSIONS
Our study was the first to demonstrate that UT-II activates the cardiac sarcolemmal NHE1 and that the phenomenon may involve, at least in part, the phospholipase C-protein kinase C-ERK pathway.
Kato
Koji
K
Department of Internal Medicine, Nippon Medical School, Tokyo, Japan. katokoji@nms.ac.jp
Yasutake
Masahiro
M
Jia
Dalin
D
Snabaitis
Andrew K
AK
Avkiran
Metin
M
Kusama
Yoshiki
Y
Takano
Teruo
T
Mizuno
Kyoichi
K
D000367:Age Factors; D000818:Animals; D048049:Extracellular Signal-Regulated MAP Kinases / Q000502:physiology; D006352:Heart Ventricles / Q000166:cytology / Q000201:enzymology / Q000378:metabolism*; D006801:Humans; D008297:Male; D032383:Myocytes, Cardiac / Q000166:cytology / Q000201:enzymology / Q000378:metabolism*; D011493:Protein Kinase C / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D012508:Sarcolemma / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology; D017923:Sodium-Hydrogen Exchangers / Q000378:metabolism*; D010738:Type C Phospholipases / Q000502:physiology; D014579:Urotensins / Q000502:physiology*
D017923:Sodium-Hydrogen Exchangers; D014579:Urotensins; C029677:urotensin II; D011493:Protein Kinase C; D048049:Extracellular Signal-Regulated MAP Kinases; D010738:Type C Phospholipases