LOCALIZATION OF 2 CLASSES OF ACETYLCHOLINE RECEPTOR-LIKE MOLECULES INSPERMS OF DIFFERENT ANIMAL SPECIES

The distribution of different classes of acetylcholine (ACh) receptor- like molecules in sperms of different invertebrate and vertebrate spec ies is described. ACh receptor molecules belong to one of two classes: muscarinic receptors (mAChRs), associated with signal transduction me chanisms in the inner domain of the cell, and nicotinic receptors (nAC hRs), capable of opening Na+ channels when activated by the ligand. Mo lecules immunologically related to mAChRs and to ACh can be identified by specific antibodies, and revealed by immunofluorescent or immunogo ld staining; the nicotinic receptor-like molecules are localised as cu rare-sensitive affinity sites for a-bungarotoxin. In all species studi ed, both classes of receptors were found, with a similar distribution. Muscarinic-like molecules were found mainly in the sperm head regions of most species; such a localisation may be correlated to a function in sperm-egg interaction, for instance in the regulation of the block to polyspermy. Nicotinic-like molecules are present mainly in the tail and in the post-acrosomal region of most animals, thus confirming the ir function in the regulation of sperm propulsion, but are also presen t at the acrosomal region of most species. The distribution patterns o f the different classes of molecules indicate that both may be involve d in sperm-egg interactions, in addition to their known function in th e regulation of sperm propulsion.