Effect of calcium on the pellet height response of Tetrahymena cilia

The pellet height response (a measure of the increase in height of the pellet of cilia obtained by brief centrifugation in the presence of ATP as compared to the absence of ATP) of Tetrahymena cilia prepared by deciliation in the presence of Ca2+ is sensitive to the concentration of free Ca2+ during the pellet height assay. The magnitude of the increase in pellet height and the sharpness of the pellet boundary both increase markedly with increasing [Ca2+]. The half-maximal effect is attained at a free [Ca2+] of about 1.5 x 10(-7) M. The pellet height assay thus measures a Ca2+-sensitive component of the ciliary motile system. The possibility that this is the Ca2+-sensitive orientation system is discussed.