Histamine is an antagonist of the acetylcholine receptor at the frog endplate

Abstract

The effects of histamine on the acetylcholine (ACh) receptor‐channel complex were examined by means of voltage‐clamp at the frog endplate. ACh was ionophoretically applied to the endplate. Histamine was added to the perfusate. Histamine (100 nM − 1 mM) reversibly depressed the peak amplitude of the ACh‐induced inward current in a dose‐dependent manner. The double reciprocal plot of the dose‐response relationship between the peak ACh current and the amount of ACh applied suggested that histamine (100 μM) depressed the ACh‐induced current in a competitive manner. Histamine prevented the specific ACh binding site within the receptor‐channel complex from binding erabutoxin, a sea‐snake venom, which binds irreversibly to the specific ACh binding site. Histamine had no detectable effects on the equilibrium potential of the endplate current but shortened the half‐decay time of the endplate current in a voltage‐dependent manner. It was therefore concluded that histamine blocks not only the specific ACh binding site but also interacts with the ACh‐channel site. The present experiments strongly suggest that histamine can act as an antagonist to modulate nicotinic cholinergic transmission.

On the histamine‐induced depolarization of the isolated superior cervical ganglion of the rat

“…A fast depolarization of this preparation can be evoked by the activation of nicotinic, GABAA and 5-HT3 receptors, so we first considered whether histamine could be activating one of these receptors. It is known that histamine interacts with the nicotinic receptor at the neuromuscular junction, albeit in an apparently competitive antagonist manner (Ariyoshi et al, 1985), but we tested for the possibility that it could activate a nicotinic response on this preparation. The resistance of this response to mecamylamine and the small effect of (+ )-tubocurarine indicated that the opening of nicotinic receptor-linked ion channels was improbable.…”