Peyer's patches (PP), specific regions of condensed lymphoid tissue in the intestine, act as the major site of environmental sampling for the intestinal immune system (Owen, 1999). Despite the fact that the epithelium overlying this tissue contains enterocytes, very little is known about ion transport across these areas of intestine. Brayden & Baird (1994) have shown that PPs from rabbit ileum exhibit atypical responses to the muscarinic agonist carbachol (CCh), but this remains an isolated phenomenon. Hence, we have set out to characterise the response of mouse PPs to CCh, the adenylate cyclase activator forskolin, and the neurotoxin veratridine.

PPs and adjacent control mucosae were prepared from the duodenum and jejunum of male 129SvJ/C57Bl6 mice, and voltage-clamped at 0mV as described previously (Cox et al., 2001). Ion transport was measured as the short circuit current (I_sc), transepithelial resistance (TER) was calculated at intermittent 1mV pulses using Ohm's law. CCh (1µM), and tetrodotoxin (TTX, 100nM) responses were recorded after 2 minutes. Maximal changes in I_sc within 10 minutes of drug addition were measured for forskolin (10µM), and veratridine (30µM); all agents were added basolaterally. Values given in Table 1 are the mean±1 s.e.m. Data groups were compared using Student's unpaired t-test.

TER and basal I_sc measured from PPs (n=26) were 29.5±3.3.cm² and 42.5±5.4µA.cm^-2 respectively. In adjacent control mucosae (n=24), these values were 11.8±1.1.cm² and 139.9±16.6µA.cm^-2 (P<0.001 for both).

The neurotoxin TTX, decreased basal I_sc in both PPs and control mucosae (Table 1). Subsequently, both CCh and forskolin induced significantly lower increases in I_sc in PPs than controls. After TTX pre-treatment, CCh still produced significantly lower increases in I_sc in PPs than controls (Table 1).

The CCh response in PPs was blunted when TTX pre-treated preparations were compared to untreated PPs (P<0.07). In the presence of TTX, the forskolin induced responses were unchanged.PP mucosae were treated with veratridine which depolarises intrinsic neurones. Veratridine induced a maintained increase in Isc in both PPs and control mucosae, however PPs displayed a significantly diminished secretory response (Table 1).

Table 1. Comparison of agonist responses in murine PPs and adjacent control mucosae. n numbers are in parentheses. *** P<0.0001, ** P<0.001, * P<0.05.

In summary, our data indicate that PPs in the small intestine exhibit higher TER and lower basal I_sc levels in comparison to the normal epithelia of the intestine. Moreover, the CCh responses in mouse small intestine were blunted, but not the reversed signature that was seen in the rabbit ileum, hence this phenotype is not conserved in the mouse. Our data demonstrate that observed responses to secretagogues, are significantly muted in PPs, which is perhaps a functional consequence of reduced epithelial cell numbers in PPs.

Brayden, D.J. & Baird, A.W. (1994) Br. J. Pharmacol, 113, 593-599.
Cox, H.M., et al. (2001) Peptides, 22, 445-452.
Owen, R.L. (1999) Sem. Immunol. 11, 157-163.

This project is funded by the BBSRC.