. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 518 S. A. ARKETT ET AL. J. FIGURE 3 A. Intracellular electrode recording from pre-oral ciliated cells of Calliostoma ligatum veligers. Horizontal scale = 50 ms. (1, 2, 3) 200 ms (4, 5), vertical scale = 10 mV. 1. Single oscilloscope sweep of a spontaneous action potential in normal seawater. Note the short duration positive phase and long duration hyperpolarizing undershoot. 2. One minute after beginning replacement of normal CaCl2 seawater with 10 mA/CoCl2 seawater. Note the loss of the hyperpolarized undershoot and the bro
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 518 S. A. ARKETT ET AL. J. FIGURE 3 A. Intracellular electrode recording from pre-oral ciliated cells of Calliostoma ligatum veligers. Horizontal scale = 50 ms. (1, 2, 3) 200 ms (4, 5), vertical scale = 10 mV. 1. Single oscilloscope sweep of a spontaneous action potential in normal seawater. Note the short duration positive phase and long duration hyperpolarizing undershoot. 2. One minute after beginning replacement of normal CaCl2 seawater with 10 mA/CoCl2 seawater. Note the loss of the hyperpolarized undershoot and the broadening of the spontaneous action potential. Spike still caused a velum wide ciliary arrest. 3. After two minutes, depolarization no longer caused velum-wide ciliary arrest, although localized "stutters" in ciliary beating were visible. 4. Three minutes in 10 mA/ CoCl2 seawater, small spontaneous EPSPs are still present. 5. Five minutes in 10 mA/CoC!2 seawater. All synaptic activity is abolished. Spikes could not be initiated by intracellular stimulation. Upon return to normal seawater, spikes return as in 1. Same electrode penetra- tion for 1-5. B. Spontaneous action potential of pre-oral cells in normal seawater (1) and about 5 minutes after the addition of 5 mA/ 4-aminopyridine (2). Horizontal scale = 20 ms, vertical scale = 10 mV. C. Action potential of pre-oral cells in normal seawater (1) and two minutes after the addition of 10 mA/ tetraethylammonium chloride. Horizontal scale = 20 ms, vertical scale = 10 mV. Pre-oral ciliated cell action potentials are reversibly reduced in amplitude and are eventually abolished when CaCl2 is replaced by an equimolar concentration of CoCl2 (Fig. 3A). Cilia beat continuously and action potentials could not be elicited by intra- cellular electrode stimulation in 10 rrLMCoCl2 seawater. Increasing concentrations of Mg++ produced a similar effect, but even at 120 mAf Mg++, a 5-10 mV depolariza- tion was still detectable. It appears
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