Ouabain blocks some rapid concentration-induced clamp acetylcholine responses onHelix neurons

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Abstract
The effects of ouabain, a potent inhibitor of Na+ - K+ ATPase, were determined on the transmembrane responses of internally dialyzedHelix neurons to rapid acetylcholine (ACh) application using the “concentration clamp” technique. Ouabain selectively depressed “A”-type responses to ACh, which are due to a selective increase in membrane permeability to chloride. In contrast, the “B”-type responses, due primarily to an increase in monovalent cation permeability, was unaffected. The blockade of the Cl- responses was not associated with a change of the reversal potential of the response. Ouabain depressed the maximal response without shifting the dose-response curve. Ouabain caused an increase in the time constant of decay of the ACh current, but the value in the presence of ouabain was not different from that of a lower concentration of ACh determined so as to give a response of the same peak amplitude. Therefore, the effect of ouabain is not on the process of receptor desensitization directly.