. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. J. R. CLAY AND A. SHRIER 5 ms OmV although small-amplitude subthreshold oscillations were still observed (Fig. 2C). Spontaneous activity was reestab- lished when the initial perfusate (pH, = ) was used (Fig. 2D). These results are consistent with a threshold (all-or- none phenomenon) for autonomous activity with pHj. The threshold was in the to range, as indicated by four experiments in which pH, was changed in increments from pH, = to In three experiments on an unrelated topic, spontaneous firing was
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. J. R. CLAY AND A. SHRIER 5 ms OmV although small-amplitude subthreshold oscillations were still observed (Fig. 2C). Spontaneous activity was reestab- lished when the initial perfusate (pH, = ) was used (Fig. 2D). These results are consistent with a threshold (all-or- none phenomenon) for autonomous activity with pHj. The threshold was in the to range, as indicated by four experiments in which pH, was changed in increments from pH, = to In three experiments on an unrelated topic, spontaneous firing was observed upon initiation of intracellular perfusion with a buffer consisting of 400 mM sucrose, 250 mM KF, B. 5 ms -50 50 ms Figure 1. (A) Action potential from a squid giant axon in control conditions (pH, = ) elicited by a 1-ms, suprathreshold current pulse. The arrow indicates a slight oscillatory rebound after the action potential. The inset illustrates a 100-ms epoch during rest (voltage scale 4X). (B) Action potential 2 mill after changing to an intracellular buffer with pH = The oscillatory rebound was considerably larger, and the membrane potential oscillated about the resting level (inset; voltage scale 4x>. (C) Initiation of spontaneous firing of action potentials, about 3 min after the change to pH, = The spontaneous activity in this preparation lasted 4 h, at which point the experiment was terminated. such as those in Figure 1 were observed in 20 out of 24 axons in which the effect was investigated. The frequency of firing at T = 5 °C. the temperature at which several of the experiments were performed, was ± Hz (n = 8; ±SD). The pH, effect was reversible, as illustrated in Figure 2. In this experiment. pH, was initially The axon fired spontaneously (Fig. 2A). The intracellular perfusate was then switched to one having a pH of (Fig. 2B). No clear effect on the electrical activity was observed 15 min after the solution change. Whe
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