1. The activity of comb plates of Pleurobrachia was analysed from cine films.
2. The interval between successive beats of a comb plate varied from several seconds to about 50 msec. in normal sea water; this variation in frequency was accompanied by a variation wave velocity. There was an almost linear relationship between wave velocity and frequency, ranging from a minimal wave velocity of about 20 mm./sec. at low frequencies to a maximal wave velocity of about 80 mm./sec. at the highest frequencies.
3. The wave velocity was accelerated at low frequencies by increased Mg2+ concentrations, by ouabain and by curare, and the same substances decreased the wave velocity at high frequencies.
4. The frequency of beat was accelerated by certain concentrations of adrenaline, serotonin, Mg2+, ouabain and curare. Decreases of frequency were found in acetylcholine (and eserine) and strychnine. These substances act on the excitability of the pacemaker.
5. It is concluded that metachronal transmission is by a flow of electric current from one comb plate to the next. Depolarization, either by a recent excitation of the comb plate or by agents like ouabain causes increased excitability and a more rapid transmission. The minimum phase difference between adjacent comb plates was about 5 msec.
6. The comb plates are almost entirely dependent on a conducted impulse for their excitation; occasionally a spontaneous excitation occurs. The membranelles of Stentor depend more on excitation within the ciliary base and less on the conducted impulse. The two systems are believed to share common features, but differ in the relative importance of these features.
7. Reverse waves involving the beating of comb plates in the normal direction were observed. The wave velocity of these waves increased only slightly over a wide frequency range. Reverse waves of this type are believed to be transmitted by mechanical contact between the comb plates.
- Copyright © 1968 The Company of Biologists Ltd.