Poly(A)+ RNA From Sheep Omasal Epithelium Induces Expression of a peptide Transport Protein(S) in Xenopus laevis Oocytes

Abstract

In order to verify the research from this

laboratory that sheep omasal epithelium

contains mRNA encoding for a peptide

transporter (s) and to determine di- to

octapeptide transport capability, poly(A)+

RNA isolated from sheep omasal

epithelium was injected into Xenopus laevis

oocytes. Poly(A)+ RNA was functionally

expressed in Xenopus oocytes 4 to 7 d

post-injection. Peptide (5 di-, 10 tri-, 6

tetra-, 2 penta-, 1 hepta-, 1 septa-, 1

octapeptide) transport capability was

measured by impaling oocytes with a

microelectrode to monitor membrane

potential (Vm). Oocytes were maintained in

pH 5.5 buffer. Peptide transport was

identified as being expressed when, in the

presence of a buffered peptide substrate (1

mM), the oocyte membrane showed

persistent depolarization (a more positive

Vm). In the absence of peptide transport,

the membrane became depolarized with the

addition of buffered substrate, but rapidly

repolarized to the resting potential. Peptide

transport was expressed for some di-, tri-,

and tetrapeptides. Measured depolarization

ranged from 9.6 mV to 42.1 mV. Larger

peptides were not transported by the

oocytes. When transport expression was

measured with the substrates in a pH 7.5

buffer, no transport occurred indicating that

transport was dependent on a proton

gradient. The data indicate that sheep

omasal epithelium contains mRNA that

code for a protein(s) capable of

proton-dependent di-, tri-, and tetrapeptide

transport. This provides further evidence

that absorption of peptides from the

ruminant stomach is possible.