| [Background]Ligustrazine (also known as Tetramethylpyrazine, IMP, C8H12N2, molecular weight 136.20) is an active alkaloid contained in the rhizome of ligustium wollichii franchat. There have been many reports on the pharmacological efficiency of TMP with respect to inhibition of platelet aggregation, scavenging oxygen free radical, diuretic, antimetastasis of tumor, improving immunity and anti-inflammatory. TMP has been widely used for the treatment of patients with cardiac and cerebral vascular diseases, nephropathy and respiratory disease. TMP has many physiological effects on digestive system: dilating blood vessel through increasing intracellular cAMP; promoting gastric secretion and suppressing the gastric contractions; TMP can also protect the pancreatic cells in acute pancreatitis by increasing blood volume, scavenging oxygen free radical and decreasing the concentration of intracellular Ca2+. TMP has also been used in China for the treatment of digestive diseases, but the effects of TMP on the secretion of HCO3- in pancreatic juice is unknown. Pancreatic juice is one of the most important digestive juices, which include digestive enzymes secreted by acinar cells, water and ions, both of which are mostly secreted by pancreatic duct epithelial cells. HCO3- plays an important role in digestve function. The secretion of HCO3- has relevance to intracellular cAMP and Ca2+. Secretin has been reported to increase pancreatic intracellular cAMP that activates protein kinase A (PKA) whichin turn stimulates the secretion of HCO3-. Recently it has also been reported that the increase of intracellular Ca2+ in pancreatic duct epithelial cells can promote the secretion of HCO3-. Some studies have demonstrated that TMP is a kind of new Ca2+ antagonist, but others shown that TMP can enhance Ca2+ influx of cardiomuscular cells. IMP could also increase the intracellular cAMP by inhibiting the activity of phosphodiesterase (PDE) to dilate the blood vessels. Because of the effectes of TMP on the intracellular cAMP and Ca2+, we speculate that TMP could affect the secretion of HCO3- greatly by affecting the concentration of intracellular cAMP and Ca2+.Aim 1. To investigate the effects of TMP on the pancreatic anion secretion in Capan-1 cell line (a kind of human pancreatic ductal cell line) and the underlying mechanisms.[Methods] The effects of TMP on the pancreatic anion secretion and the underlying mechanisms were studied by short-circuit current (Isc) technique.[Results] 1. Basolateral addition of TMP produced a dose-dependent increase in Isc (EC50=1.56mmol), which contained a fast transient Isc response followed by a slow decay. 2. Removal of extracellular HC03" or Na* blocked the TMP-induced increase in Isc by about 82%(P<0. 001) and 54% (P<0. 05) respectively, however the removal of external Cl- increased the response by about 60% (P<0. 05). 3. Apical application of CY channels blockers, DPC, decreased the response by about 59%(P<0. 001), but apical application of Ca2+-dependent Cl- channels blockers, DIDS, didn' t(P>0. 05). 4. Basolateral pretreatment with H-DIDS, the inhititor of Na*- HCO:) cotransporter (NBC), decreased the response by about 56% (P<0. 01) whereas the pretreatment with acetazolamide didn' t(P>0. 05). 4. Apical application of Ca2+ chelator, BEPTA-AM, didn't affect the TMP - induced Isc (P>0. 05) .5. The pretreatment with phosphodiesterase inhibitor, IBMX, decreased theTMP-induced Isc by 93%(P<0.001), but the apical addition of MDL12330A, an adenylate cyclase inhibitor, or the apical addition of H89, the inhibitor of PKA, didn' t affect the response (P>0. 05) .[Conclusions] 1.TMP could promote Capan-1 to secrete HCO3- which mostly are transported by basolateral NBC and minorly may come from the diffusion of CO2 across the basolateral membrane. 2. The TMP-induced secretion of HC03" is meadiated by cystic fibrosis transmembrane conductance regulator (CFTR) but not C1-HCO3- exchanger (AE). 3. The cGMP but not cAMP and Ca2+ is perhaps involved in the TMP-induced HC03~ secretion. |
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