Branched Short-Chain Fatty Acid Isovaleric Acid Causes Colonic Smooth Muscle Relaxation via cAMP/PKA Pathway
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Isovaleric acid (IVA) is a 5-carbon branched-chain fatty acid present in fermented foods and produced in the colon by bacterial fermentation of leucine. We previously reported that the shorter, straight-chain fatty acids acetate, propionate and butyrate differentially affect colonic motility; however, the effect of branched-chain fatty acids on gut smooth muscle and motility is unknown.
To determine the effect of IVA on contractility of colonic smooth muscle.
Murine colonic segments were placed in a longitudinal orientation in organ baths in Krebs buffer and fastened to force transducers. Segments were contracted with acetylcholine (ACh), and the effects of IVA on ACh-induced contraction were measured in the absence and presence of tetrodotoxin (TTx) or inhibitors of nitric oxide synthase [L-N-nitroarginine (L-NNA)] or adenylate cyclase (SQ22536). The effect of IVA on ACh-induced contraction was also measured in isolated muscle cells in the presence or absence of SQ22536 or protein kinase A (PKA) inhibitor (H-89). Direct activation of PKA was measured in isolated muscle cells.
In colonic segments, ACh-induced contraction was inhibited by IVA in a concentration-dependent fashion; the IVA response was not affected by TTx or L-NNA but inhibited by SQ22536. Similarly, in isolated colonic muscle cells, ACh-induced contraction was inhibited by IVA in a concentration-dependent fashion and the effect blocked by SQ22536 and H-89. IVA also increased PKA activity in isolated smooth muscle cells.
The branched-chain fatty acid IVA acts directly on colonic smooth muscle and causes muscle relaxation via the PKA pathway.
KeywordsColon Smooth muscle Isovaleric acid Branched-chain fatty acid Cyclic AMP Adenylyl cyclase Protein kinase A SQ22536 H-89 Tetrodotoxin Nitric oxide synthase L-N-nitroarginine
This work was supported by grants DK34153 (JR Grider) and DK28300 and DK15564 (KS Murthy) from the National Institute of Diabetes and Kidney Diseases.
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Conflict of interest
The authors declare that they have no conflict of interest.
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