The molecular mechanism of neural induction: neural differentiation of Triturus ectoderm exposed to Hepes buffer.

Ectoderm was isolated from early gastrula stages of Triturus alpestris and cultured in salt solution buffered with either bicarbonate or Hepes as the principal buffer substance. When bicarbonate was the principal buffer substance or when bicarbonate was omitted, the isolated ectoderm formed atypical epidermis. When Hepes was added as a buffer substance, neural tissue was formed in a high percentage of cases. The differentiation of neural tissue depends on the pH of the Hepes buffer. Hepes in the protonated form, which prevails at lower pH, seems to evoke neural differentiation at a much higher rate. Hepes could either enhance the NA/H antiport system or it could directly bind to plasma membrane constituents. In both cases conformational changes in the plasma membrane could generate signals which finally lead to neural differentiation.