. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 190 J. R. CLAY AND A. SHRIEK. liAcm"2 J Figure 4. Simulations of pH,-induced excitability. Steady-state current-voltage relations are shown for pH, = and pH, = The sole difference in the model for the two conditions is in the leak current conductance, which is and mS • cm~- for pH, = and respectively. The equilibrium potential, that is. the point where the current-voltage relation crosses the voltage axis, is stable for pH, , as indicated by the trajectory in the inset adjacent to thi
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 190 J. R. CLAY AND A. SHRIEK. liAcm"2 J Figure 4. Simulations of pH,-induced excitability. Steady-state current-voltage relations are shown for pH, = and pH, = The sole difference in the model for the two conditions is in the leak current conductance, which is and mS • cm~- for pH, = and respectively. The equilibrium potential, that is. the point where the current-voltage relation crosses the voltage axis, is stable for pH, , as indicated by the trajectory in the inset adjacent to this point. (The scales are 5 mV and 2 p,A • cm"2). An action potential elicited by a suprathreshold current pulse for this condition is shown below the current-voltage relation. (The scales are 50 mV and I ms.) The equilibrium point for pHj = is unstable, as illustrated by the adjacent trajectory. (Same scales as the current-voltage trajectory for pH, = ) This trajectory spiraled out to the limit cycle described by the spontaneous action potentials shown adjacent to the current-voltage relation. Scales are 50 mV and 20 ms. pH, as compared to pH, (symbols (•) in Fig. 3B). This result suggests that a change of pH, might affect the third component of the Hodgkin and Huxley (1952) model of the action potential, namely the background, or "leak" current, /,. In particular, the resistance measurements in Figure 3 imply that the leak component is reduced by an increase in pH,. This idea has precedence in the work of Bevan and Yeats (1991), who reported the activation of a sustained, nonspecific cation conductance in a subpopula- tion of rat dorsal root ganglion neurons by extracellular protons. Alkaline pH would reduce the amplitude of this conductance. The background current in squid giant axons also consists of a small-amplitude tetrodotoxin-sensitive sodium ion cur- rent (referred to as /N;|P) that is activated at relatively negative potentials, ab
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
