Comparative study of cholinesterase in two snails Pila globosa and Lymnaea acuminata

Enzymatic activity of acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) was measured in the nervous and cardiac tissue of two snails Pila globosa and Lymnaea acuminata. Data on substrate specificity, enzyme kinetic constants and specific enzyme inhibitors indicated that, L. acuminata possessed both AChE and BuChE, while, P. globosa had only AChE. Pharmacological experiments carried out on isolated organs of the two snails indicated that isolated organs of P. globosa were sensitive to low doses of acetylcholine (ACh) and to relatively higher doses of butyrylcholine (BuCh). The responses elicited by ACh could be enhanced by eserine but that of BuCh could not be increased by ethopropazine which has been shown to be a specific inhibitor of BuChE in snails. Isolated hearts of L. acuminata on the other hand, were more sensitive to BuCh as compared to ACh. The BuCh effect was enhanced by ethopropazine while the effect of both ACh and BuCh increased by prior application of eserine. There is a correlation between the occurrence of the two types of cholinesterase (ChE) and the sensitivity of the isolated organs to a specific substrate of these enzymes suggesting a possible correlation between transmitters and cholinesterase system.