Early appearance and possible functions of non-neuromuscular cholinesterase activities
1. Methiodide derivatives of serotonin blockers--inmecarb and KYur-14 which poorly penetrate the cells specifically affect the pattern of cleavage division in half-embryos of Paracentrotus lividus and Scaphechinus mirabilis. 2. Specific [3H]8-OH-DPAT binding under conditions strictly limiting penetration of the ligand into the cells of Strongylocentrotus intermedius was also shown (Kd approximately 3 x 10(-10) M for a site with the greatest affinity). 3. On the basis of the data obtained it is concluded that neurotransmitter-specific membrane receptors may be present in sea urchin embryos during cleavage divisions. The "protosynapse" hypothesis is proposed which suggests the existence of a specific structure responsible for early blastomere interaction involving transmitters.