Abstract
Spontaneous contractions of the circular muscles of the asteroid Coscinasterias calamaria were measured by observing the rate of contraction of strips of the aboral body wall taken from unanaesthetised animals. Contractions in artificial sea water, high Ca2+, high K+, K+ free and Mg2+ free media were rapid and complete. High Mg2+, Ca2+ free, low Na+ and distilled water media inhibited contractions. Animals were anaesthetized in MS222 and the contraction of tissue strips in media containing the anaesthetic was assayed. Anaesthetized tissues exhibited very small contractions in the first 100–200s of the assay due to the stimulus of excision. MS222 effectively blocked all other contractile response. Anaesthetized tissue strips rapidly recovered contractility when placed in artificial sea water without the anaesthetic.
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