Synthetic organic pH buffers can support fertilization of guinea pig eggs, but not as efficiently as bicarbonate buffer.

Bicarbonate ions (HCO3-) in the medium are not absolutely essential for the fertilization of guinea pig eggs. However, fertilization takes place most efficiently in HCO3- -buffered medium. Capacitation, the acrosome reaction, and zona penetration by spermatozoa can occur in HCO3- -free media with synthetic organic buffers (i.e., MOPS, TES, HEPES, Tris, and TAPSO) but not as efficiently as in the HCO3- -buffered medium. It appears that HCO3- functions as more than just a pH-buffering molecule.