"It could have been something as simple as a short chain of amino acids embedded in a cell membrane which, when pushed on (by a small vibrating bone, for example), created a hole in the membrane that allowed ions to flow in, starting the signaling cascade. Short chains of amino acids were certainly around very early on, and any lipophyllic sequences would embed in a cell membrane."
What does your last statement have to do with the likelyhood that the DNA would encoded such changes as to embed an amino acid sequence in the cell membrane?
Now if you had said, 'a genetic mutation created lipophyllic sequences that would then embed in a cell membrane', then we would not have had all these replies back and forth.
I apologize for not understanding what you meant to say, as oppose to what you actually wrote.
Now we can move on the the odds that such a scenario might happen. :)