Alteration of sphingosine-1-phosphate with aging induces contractile dysfunction of colonic smooth muscle cells via Ca -activated K channel (BK ) upregulation.

BACKGROUND

Age-associated changes alter calcium-activated potassium channel (BK ) expression of colon. Sphingolipids (SLs) are important cell membrane structural components; altered composition of SLs may affect BK expression. This study investigated the mechanism by which sphingosine-1-phosphate (S1P) contributes to age-associated contractile dysfunction.

METHODS

Fifty male Sprague Dawley rats of different ages were randomly assigned to five age-groups, namely 3, 6, 12, 18, and 24 months. BK expression, S1P levels, and phosphorylated myosin light chain (p-MLC) levels were tested in colonic tissues. In the absence and presence of S1P treatment, BK expression, p-MLC levels, and intracellular calcium mobilization were tested in vitro. BK small interfering RNA (siRNA) was used to investigate whether p-MLC expression and calcium mobilization were affected by BK in colonic smooth muscle cells (SMCs). The expressions of phosphorylated protein kinase B, c-Jun N-terminal kinases (JNKs), extracellular-regulated protein kinases, nuclear factor kappa-B (NF-κB), and protein kinase C (PKC ) were examined to investigate the correlation between S1P and BK .

KEY RESULTS

Sphingosine-1-phosphate levels and sphingosine-1-phosphate receptor 2 (S1PR2) and BK expressions were upregulated and p-MLC expression was downregulated in the colonic tissues, age dependently. In the cultured SMCs, S1P treatment increased BK expression and reduced calcium concentration and p-MLC was observed. BK siRNA increased calcium concentration, and p-MLC levels significantly compared with control. We also showed that S1P upregulated BK through PKC , JNK, and NF-κB pathways.

CONCLUSIONS AND INFERENCES

In conclusion, S1P and S1PR2 participate in age-associated contractile dysfunction via BK upregulation through PKC , JNK, and NF-κB pathways.