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Received for publication August 11, 2006.
Revised December 1, 2006.
Accepted for publication December 1, 2006.
1-adrenergic stimulation
Multiple stimuli of physiological and pathophysiological
significance, including 
1-
adrenoceptor agonists, stimulate the cardiac sarcolemmal
Na+/H+ exchanger NHE1 through
activation of the MEK-ERK-RSK signaling cascade.
However, the individual contributions of ERK and RSK,
which can each phosphorylate the NHE1 regulatory domain,
to such stimulation are unknown. In the present study,
we have used the novel RSK inhibitor fmk to determine
the role of RSK as a direct regulator of NHE1
phosphorylation and activity in response to
1-adrenergic stimulation, in ventricular
myocytes isolated from the adult rat heart. Initial
experiments confirmed that pretreatment of myocytes with
fmk before exposure to the 1-
adrenoceptor agonist phenylephrine inhibited RSK C-
terminal kinase activity and thereby RSK N-terminal
kinase activation, without affecting MEK or ERK
activation. Pretreatment of myocytes with fmk also
inhibited phenylephrine-induced increases in NHE1
phosphorylation and the rate of NHE1-mediated
H+ efflux under conditions of intracellular
acidosis. These findings reveal, for the first time to
our knowledge, that RSK is the principal regulator of
NHE1 phosphorylation and activity following
1-adrenergic stimulation in adult myocardium.
Key words:
Adrenergic, Protein Kinases (other), Fluorescence techniques, Ischemia/Reperfusion, Tissue hypertrophy
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