The effect of enzyme substrates and pharmacological agents on nematocyst discharge

Lentz, T.L.; Barrnett, R.J.

Journal of Experimental Zoology 149: 33-38


ISSN/ISBN: 0022-104X
PMID: 14464028
DOI: 10.1002/jez.1401490104
Accession: 025748692

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The effects of enzyme substrates and inhibitors and of neuropharmacological agents on nematocyst discharge are reported in this paper. The control situation of mechanical stimulation of the tentacles in the absence of chemical mediators resulted in virtually no nematocyst discharge. Addition of organic phosphates to the medium produced nematocyst discharge with mechanical stimulation. Enzymatic inhibitors practically eliminated the discharge produced in this manner. In regard to the nervous system, acetylcholine produced a massive discharge which was augmented by eserine and inhibited by hexamethonium and tubocurare. Enzyme inhibitors, exclusive of cholinesterase inhibitors, decreased the response that was obtained with acetylcholine but hexomethonium did not alter the discharge produced by enzyme substrates. Epinephrine, 5-hydroxytrypt-amine, norepinephrine, and histamine caused release of nematocysts and were the only agents to affect holotrichous isorhizas. These experiments indicate that mature nematocysts containing strategically placed enzymes are able to respond (providing mechanical stimulation also occurs) to chemical reagents which serve as enzyme substrates and therefore as effector substances. In addition, the nervous system of hydra appears to play a significant role in nematocyst discharge. Each type of stimulus appears to be a different subliminal mechanism in which chemical stimulation does not affect the nervous system and the latter does not affect chemical stimulation, but all stimuli, including mechanical, appear to act through a chain of enzymatic events.