Electrical responses to water‐soluble components of fish mucus recorded from the cnidocytes of a fish predator,Physalia physalis

Abstract

Physalia physalis, the Portuguese man of war, consumes mostly fish and fish larvae. Intracellular recordings from nematocyst‐containing cells (cnidocytes) in small pieces of Physalia tentacle were used to quantify the electrical responses to diluted and filtered fish skin mucus, 1–100 x 10‐6 M amino acids, monosaccharides, and nucleosides, and seawater, which were delivered upstream of the tissue. Seawater caused responses (one pulse only) in about 10% of the applications. Fish mucus extract elicited responses in all applications, producing 1–18 depolarizing pulses (20 mV maximum amplitude). The pulses were characteristic of post‐synaptic potentials (EPSPs). Lucifer yellow and biocytin dye injections showed that the cnidocytes were not electrically coupled. Simultaneous records from two cnidocytes following mucus applications were identical.We propose, therefore, that the chemoreceptors are not on the cnidocytes, but are probably on sensory neurons that innervate clusters of cnidocytes. A < 3,000 MW fract...