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Problem: Uptake of anions such as chloride and bicarbonate across the wall of the ovine and bovine
rumen is essential for the maintanance of ruminal homeostasis and for balancing the salivary inflow of
buffer. In a previous publication, we identified an anion conductance in isolated cells of the ruminal
epithelium (Am J Physiol Gastrointest Liver Physiol 289: 3, G508-20, 2005). In the current study, we tried
to characterize this conductance in more detail.
Material and methods: Ruminal epithelial cells were isolated from ruminal tissue and cultured
according to established methods. Whole cell and single channel currents were measured with the
Results: Cells were filled with a Na-gluconate solution and perfused with equimolar NaCl solution.
When chloride was replaced with gluconate, outward current at 100 mV dropped to 33 ± 4% of the
original value (n = 25) and cells were depolarised from -32 ± 1.2 mV to 2.9 ± 0.8 mV (p < 0.0001).
Replacement of chloride with nitrate (130 mM or 65 mM) had no effect on outward current (105 ± 16%, n
= 9 and 104 ± 11%, n = 4) or reversal potential (p > 0.05). Conversely, replacement of chloride by HCO3
reduced outward current to 60 ± 6% and reduced reversal potential to -21 ± 2 mV (n = 6; p = 0.01 versus
NaCl and p = 0.001 versus Na-gluconate). DIDS (1 mM and 100 μmol) blocked outward current in NaCl
solution to 44 ± 13% and 82 ± 7% (n = 16 and n = 5, respectively; p = 0.02 and p = 0.03). Excised inside
out patch-clamp experiments in symmetrical and assymetrical NMDG-anion solutions revealed channels
with a conductance of 350 ± 7 pS for chloride (n = 5).
Conclusion: We conclude that isolated ruminal epithelial cells express anion channels with p(Cl-) ≈
p(NO3-) > p(HCO3-) > p(gluconate-). We propose that these channels may play a role in the efflux of
chloride and HCO3- across the basolateral membrane of the ruminal epithelium.