ABSTRACT
We have previously shown that chemicals including acetylcholine (ACh) induce a reversible constriction of the external openings of the madreporite of echinoids (Takahashi & Tamori, Echinoderm Biology, Burke et al. eds., 1988, p.814). In order to study the mechanism of this response, we have developed a preparation which enables us to observe the changes in shape of the soft tissue lining the madreporic pores in profile under a microscope. Using a razor blade, we excised a thin slice of tissue from the aboral surface of the madreporite of Hemicentrotus pulcherrimus. The tissue was then treated with sea water containing 0.2% collagenase for 1 hour at 30°C, after which the soft tissue, consisting of several tubular linings of the madreporic pores connected with the aboral epithelial tissue, was separated from the calcareous skeleton by gentle lifting with an eyelash. A glass needle was used to isolate a single pore tube. The isolated tube was observed with a differential interference microscope. Using this preparation, we were able to observe the lumen and the lining of the pore canal from the lateral aspect. The lumen was densely covered with cilia which beat continuously in the aboral direction. When 10−5M ACh was applied to the preparation, the lumen decreased in diameter and the wall of the tube increased in thickness within 1 minute. The response was reversible; both the diameter of the lumen and the thickness of the wall returned to their original value shortly after removal of the ACh. The direction of ciliary beating was not changed by ACh. The preparation seems to be useful for further physiological studies on the function of the madreporite.
