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Regulation of the Pleuronectes americanus Na+/H+ exchanger by osmotic shrinkage, beta-adrenergic stimuli, and inhibition of Ser/Thr protein phosphatases.

Abstract：

:The ubiquitous Na+/H+ exchanger NHE1 is regulated by protein phosphorylation events, but the mechanisms involved are incompletely understood. We recently cloned NHE1 from the red blood cells of the winter flounder, Pleuronectes americanus (paNHE1), and demonstrated its activation by osmotic cell shrinkage, beta-adrenergic stimuli, and the Ser/Thr protein phosphatase PP1 and PP2A inhibitor calyculin A(CLA) (Pedersen et al. [2003] Am. J. Physiol. 284, C1561-C1576). Here, we investigate the mechanisms involved in paNHE1 activation by these stimuli. Osmotic shrinkage and CLA were only partially additive in their effects on paNHE1 activity, and CLA-mediated paNHE1 activation was inhibited by osmotic cell swelling. Activation by the beta-adrenergic agonist isoproterenol (IP) was fully additive to activation by osmotic shrinkage or CLA. IP-mediated, but neither shrinkage- nor CLA-mediated paNHE1 activation were associated with an increase in cellular cyclic adenosine monophosphate (cAMP) level. IP-mediated activation was partially blocked by the protein kinase A (PKA) inhibitor H89 (10 microM), whereas shrinkage- and CLA-mediated activation were unaffected. All three stimuli activated paNHE1 in a manner unaffected by inhibitors of protein kinase C (calphostin C, 5 microM) and protein kinase G (KT5823, 10 microM) as well as of myosin light chain kinase (ML-7, 10 microM). IP-mediated, but not shrinkage-mediated, paNHE1 activation was associated with an increase in serine phosphorylation of the paNHE1 protein. It is suggested that paNHE1 activation by osmotic shrinkage and by PP1/PP2A inhibition involves partially convergent signaling pathways, whereas activation of paNHE1 by beta-adrenergic stimuli is mediated by a separate pathway.

journal_name

Cell Biochem Biophys

journal_title

Cell biochemistry and biophysics

authors

Holt ME,King SA,Cala PM,Pedersen SF

doi

10.1385/CBB:45:1:1

subject

Has Abstract

pub_date

2006-01-01 00:00:00

pages

1-18

issue

eissn

1085-9195

issn

1559-0283

pii

CBB:45:1:1

journal_volume

pub_type

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Regulation of the Pleuronectes americanus Na+/H+ exchanger by osmotic shrinkage, beta-adrenergic stimuli, and inhibition of Ser/Thr protein phosphatases.