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Background: Short chain fatty acids are ample products of ruminal fermentation, with rapid absorption across the ruminal wall being central to the energy supply of ruminants. Both uptake of the uncharged species via diffusion and transport of the anion via specific proteins have been suggested. Since the interpretation of electrophysiological effects observed in Ussing chamber studies is difficult (1), we investigated the impact of acetate on conductances of isolated cells.
Methods: Isolated cells of the sheep ruminal epithelium were filled with a physiological K-gluconate solution and monitored for the effects of acetate (130 mmol/l) on membrane currents and capacitance using the patch clamp technique.
Results: In physiological NaCl solution, replacement of chloride by acetate (pH 7.4) resulted in a stimulation of inward current (n = 14, p = 0.04), with stimulatory effects on outward current visible in 7 of 14 cells tested. Changes in reversal potential were not significant. In subsequent experiments, Na was replaced by K as the dominant cation, resulting in a significant depolarization from -29 +/- 3 mV to -9 +/- 3 mV (n = 19, p < 0.001). Replacement of chloride by gluconate resulted in a further depolarization to -1 +/- 2 mV (n = 18, p = 0.01). Replacement of gluconate by acetate led to a reversal potential that was slightly, but not significantly lower than this value (-4 +/- 2 mV, n = 15, p = 0.09). Both inward current and outward current were twice as high in K-acetate solution as in either KCl or K-gluconate solution (p<0.001). Capacitance of the cells did not change significantly.
Conclusion: The data demonstrate that exposure to acetate activates the potassium conductance(s) of ruminal epithelial cells. Additional interactions of acetate with the chloride conductance of the ruminal epithelium (2)(3) should not be ruled out.
1) Gabel G; Aschenbach JR; Muller F. (2002). Anim Health Res Rev. 3(1):15-30
2) Abdoun K; Stumpff F; Wolf K; Martens H (2005). Am J Physiol. 289(3):G508-20
3) Leonhard-Marek S; Breves G; Busche R (2006). Am J Physiol. 291(2):G246-52.
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