LYSOZYME ACTS AS A CHEMOREPELLENT AND SECRETAGOGUE IN PARAMECIUM BY ACTIVATING A NOVEL RECEPTOR-OPERATED CA++ CONDUCTANCE

Using combined intracellular recordings and behavioral bioassays, it w as found that lysozyme has two different effects in Paramecium, depend ing upon the concentrations used. At low concentrations (0.5 nM to 1.0 mu M) it acts as an effective chemorepellent that causes reliable ele ctrophysiological changes. Lysozyme-induced somatic depolarizations, i solated by blocking K+ channels with Cs-TEA, showed concentration depe ndencies that were well correlated with chemorepulsion. Ion dependency experiments showed that these were Ca++ based depolarizations. Additi on of either Na+ or Mg++ improves chemorepulsion by providing addition al depolarizations, Both the depolarizations and chemorepulsion were b locked by 10 mu M neomycin, suggesting that the depolarization is nece ssary for this chemosensory transduction event. At higher concentratio ns (100 mu M), lysozyme is a secretagogue. A transient inward current, recorded in Ca++ alone solutions with Cs-TEA present, was seen in res ponse to high lysozyme concentrations. The amplitude of this inward cu rrent was well correlated with exocytosis. Addition of neomycin (1.0 m M) eliminated both the inward current and exocytosis, suggesting a cau sal relationship, Neither amiloride or W-7, compounds previously sugge sted to affect the electrophysiological responses to secretagogues, ha d any significant effects, The mucopolysaccharide hydrolysis activity of lysozyme was not required for any of these responses. We propose th at Paramecium have a high affinity receptor on the body plasma membran e that responds to either lysozyme or a related compound to cause an i ncrease in a novel body Ca++ conductance. This receptor-operated Gate conductance causes membrane depolarization and chemorepulsion at low c oncentrations and triggers a sufficient Ca++ in-flux at high concentra tions to cause exocytosis.