Calcium activation of macrocilia in the ctenophoreBeroë

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Abstract
Macrocilia on the lips of the ctenophoreBeroë are usually quiescent, but can be activated to beat rapidly and continuously by various stimuli. During feeding, macrocilia beat actively and serve to spread the lips ofBeroë over its prey. Vigorous, repetitive mechanical stimulation of the lips evokes widespread activation of macrocilia via a pathway that is probably neural. Extracellular electrical stimulation (DC or bipolar pulse-trains) elicits immediate activation of macrocilia on lip pieces, but not on dissociated cells. Macrocilia on lip pieces are activated to beat by high KCl artificial sea water (ASW), but not by high KCl Ca-free ASW. Continuous beating for long periods is also elicited by high Ca ASW or Mg-free ASW, but not by Ca-Mg-free ASW. Addition of La, Cd, Co or Mn (10 mM) to high KCl ASW reversibly blocks activation. Verapamil, D-600, nifedipine, or BAY K 8644 (10 μM) has no effect on KCl-induced activation, but the anticalmodulin drug W-7 (10 μM) reversibly inhibits beating. Mild heat treatment dissociates macrociliary cells from lip tissue. Such isolated macrociliary cells usually beat continuously in normal sea water, and swim in circular paths. Ca-free ASW, or addition of Co or Mn to ASW, inhibits beating of dissociated cells. High KCl ASW activates beating of quiescent, isolated macrociliary cells. Ca-Mg-free ASW inhibits beating of dissociated macrociliary cells, and return to Mg-free ASW activates motility, allowing one to activate macrocilia on isolated cells simply by addition of Ca. These results indicate that sensory stimuli associated with feeding may excite the pharyngeal nerve net, thereby depolarizing macrociliary cells and opening voltage-sensitive Ca channels which mediate a Ca influx responsible for activation of beating.