PRESENCE OF THE NHE(3) ISOFORM OF THE NA+ H+ EXCHANGER IN HUMAN GALLBLADDER/

1. In man and in various animal species, absorption of NaCl from bile by the gallbladder mucosa is associated with luminal proton secretion, A similar absorption of NaCl in small intestine, colon and renal tubu le is related, at least in part, to the presence of the NHE(3) isoform of the Na+/H+ exchanger. This work was designed to find out whether N HE(3) is also present in human gallbladder. 2. At surgery, 100-200 mg of the gallbladder wall was obtained from patients treated by cholecys tectomy for gallstones. After isolation of the mucosa, total RNA was e xtracted and submitted to reverse transcription-polymerase chain react ion with two primers: 5'-AAGCCICTGGTGCAGTGGCTGAAGG-3' and 5'-GGAGTCCTT IAAGTCGGCIAAGCTGGGC-3', designed to amplify a sequence of 645 bp of ra bbit NHE(3) mRNA (642 bp in man), RNA from human liver and from rabbit heart, neither of which, contain NHE(3), and human ileal RNA, which d oes contain NHE(3), were used as controls. 3. RNA extracted from the m ucosal moiety of the gallbladder wall gave an amplification product of about 645 nucleotides, Controls gave the expected negative or positiv e results. Sequencing of the amplified RNA showed it was almost identi cal to previously determined sequences of NHE(3) in other human tissue s. 4. It is concluded that the mucosa of human gallbladder contains th e mRNA of NHE(3) isoform. This isoform could therefore play a role in sodium absorption from bile.