Effects of cyclic nucleotides and intracellular Ca on voltage-activated ciliary beating in Paramecium

Injections of cAMP and cGMP up to millimolar concentrations caused no detectable changes in the frequency-voltage relationship. Injection of Ca super(2+) into the cell clamped at the resting potential caused a transient anteriad ciliary reorientation and a simultaneous increase in the beating frequency. Injection of EGTA was ineffective in relation to frequency for several minutes. After this time, hyperpolarization- and depolarization-activated frequency responses of EGTA-injected cells were increasingly inhibited. A posterior contraction of the cell diameter was noticed upon membrane hyperpolarization. The contraction coincided in time with the increase in beating frequency. The results support the view that the voltage-dependent augmentation of the ciliary beating rate is not directly mediated by an intracellular increase in either cAMP or cGMP.