| Background:Sphincter of Oddi (SO) is located in the distal part of bile duct. It is introduced into duodenum but different from duodenal smooth muscle. It is an elaborate muscle structure with various biological functions. Under the action of hormone and nerves, SO can contract and relax coordinately. It plays key roles in regulation of gallbladder peristalsis and bile export and in maintenance of normal hydraulic pressure of biliary tract. The dysfunction of SO may be one cause for biliary tract diseases, pancreatic diseases and gastrointestinal diseases. Wei JG et al found that hypercholesterolemia (HC) could cause sphincter of Oddi dysfunction (SOD) which in fact damaged the normal contractility of SO and kept SO in a spasmic state. The further study indicated that the overloading of intracellular Ca2+ concentration ([Ca2+]i) may be one of the most important reasons for SOD in HC rabbit. But the mechanism is still poorly understood.AIM:To observe the effects of HC on tension and contractility of SO, we prepared isolated SO rings of HC rabbits and recorded all kinds of changes using routine vascular perfusion system in vitro; then we observed the change of the potassium channels and calcium channels in SO of HC rabbits tone via using K+ and Ca2+ channel blockers.Materials and Methods:Twenty-four New Zealand female rabbits were divided randomly into two groups: the control group (CON) and the hypercholesterolemia group ( HC ), n=12 for each group. The rabbits in CON group were fed with normal diet, while the rabbits in HC group were fed with hypercholesterol diet. Both groups were fed for 8 weeks before sphincter of Oddi muscle rings were dissociated from both groups in vitro. The following experiments were performed after the best resting tension of the SO rings was measured via using the system of routine vascular perfusion in vitro.Automatic contractility and tension of the SO rings of both groups were observed respectively. Then the contraction responses evoked by KC1 were measured.After administration of KC1 (60mmol/L) to the SO rings, the relaxation effect of sodium nitroprusside (SNP) on both groups was measured.Contraction responses of the SO rings of both groups to the special potassium channel blockers, tetraethylammonium chloride(TEA) and 4-aminopyridine (4-AP), were recorded respectively; then we observed changes of the large conductance calcium activated potassium channels (BKca) and the voltage dependent potassium channels (Kv) of SO smooth muscle cells from both groups using the routine vascular perfusion system in vitro.Relaxation responses of the SO rings of both groups to calcium channel blocker nifedipine (Nif) were recorded , then we observed change of the longlasting voltage dependent calcium channel (L -VDCs).The SO rings of both groups were incubated in 37 solution of Krebs ( free of Ca2+ ) for Smins, then contraction responses of the SO rings evoked by Ca2+ (2.5 mmol/L) were observed .Results:In contrast with control group, the automatic contractile frequency of HC group was increased (P<0.05, t=2.86) and the automatic contractile amplitude of SO was decreased (P<0.05, t=2.48) .Administrating KC1 from 10 mmol/L to 90 mmol/L, we found that the tension of SO rings evoked by KC1 of low concentration (10-40 mmol/L) was significantly higher in HC group than in control group (P<0.01, t=4.01) ; however, the maximum tension had no difference between the two groups and both groups could be completely relaxed by Nif (3 mol/L).In contrast with the control group, relaxation responses of SO rings in HC group to SNP (0.1 nmol/L ~ 1 mmol/L) weremarkedly decreased after the administration of KCI (60mmol/L) in HC group (P<0.01,r=5.12) .The contraction responses of SO rings to TEA (BKca blocker) showed no significant differences between HC and control groups; however, in contrast with control group, the ratio of the contraction responses induced by TEA (0.1-10 mmol/L) to the contraction responses induced by 60 mmol/L KCI was increase...
|
PDF Full Text Request