ðɪ ˈeɪkwɪəs fˈeɪz bᵻtwˌiːn ðiːz tˈuː mˈɛmbɹeɪnz kænˈɑːt biː kɹˈɔst baɪ ðə lˌɪpəfˈɪlɪk kəlˈɛstɚɹˌɑːl, ʌnlˈɛs sˈɜːʔn̩ pɹˈoʊtiːnz ɐsˈɪst ɪn ðɪs pɹˈɑːsɛs.
The aqueous phase between these two membranes cannot be crossed by the lipophilic cholesterol, unless certain proteins assist in this process.