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Pflügers Archiv

, Volume 427, Issue 1–2, pp 129–135 | Cite as

Modulation of the inhibitory action of ATP on acetylcholine-activated current by protein phosphorylation in rat sympathetic neurons

  • Ken Nakazawa
Molecular and Cellular Physiology

Abstract

Modulation by protein phosphorylation of the relation between acetylcholine (ACh)-activated current (IACh) and adenosine triphosphate-(ATP)-activated current (IATP) was investigated with the whole-cell voltage-clamp technique in rat sympathetic neurons. During simultaneous activation by 100 μM ATP of an inward current, the current evoked by 100 μM ACh was reduced to 60–70% of that in the absence of ATP. Effects of compounds that are known to modulate protein phosphorylation were tested by including them in the intracellular solution. The reduction ofIACh by ATP was not observed when K252a (1 μM), a non-selective protein kinase inhibitor, adenosine 5′-O-(3-thiotriphosphate) (ATP[γS], 1 mM) orα,β-methylene ATP (1 mM) were included in the intracellular solution. Activators of protein kinases, adenosine 3′,5′-cyclic monophosphate (cAMP, 100 μM), guanosine 3′,5′-cyclic monophosphate (cGMP, 100 μM), phorbol 12-myristate 13-acetate (PMA, 1 μM), also abolished the reduction by ATP ofIACh. The effects of okadaic acid, a protein phosphatase inhibitor, were paradoxical: okadaic acid (2 μM) itself abolished the reduction by ATP ofIACh but it “antagonized” the abolishment by cAMP or cGMP of the reduction ofIACh. Okadaic acid did not affect the disappearance of the reduction ofIACh by ATP in the presence of intracellular PMA. The results suggest that the interaction betweenIACh andIATP is regulated by protein phosphorylation/dephosphorylation. Possible mechanisms underlying the effects of these modulators of protein phosphorylation are discussed.

Key words

Nicotinic receptor channels ATP-activated channels Voltage clamp Protein phosphorylation 

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Copyright information

© Springer-Verlag 1994

Authors and Affiliations

  • Ken Nakazawa
    • 1
  1. 1.Department of NeurobiologyHarvard Medical SchoolBostonUSA

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