Effect of cholesterol liposomes on calcium mobilization in muscle cells from the rabbit sphincter of Oddi.

AIM: To analyze the influence of cholesterol liposome on the Ca2+ mobilization of cultured muscle cells in the rabbit sphincter of Oddi's. METHODS: New Zealand rabbit was sacrificed and the sphincter of Oddi (SO) segment was obtained aseptically. The SO segment was cut into pieces and cultured in DMEM solution. Then the smooth muscle cells were subcultured, and the 4th-7th passage cells were used for further investigation. The intracellular Ca2+ increase was measured under confocal microscope after the addition of 20 mmol x L(-1) KCl, 10(-7) mol x L(-1) acetylcholine and 10(-7) mol x L(-1) cholecystokinin, and different antagonists were added to analyze the Ca2+ mobilization pathway. After the cells were incubated with 1g x L(-1) cholesterol liposome (CL)(molar ratio was -2:1), the intracellular Ca2+ increase was measured again to determine the effect of CL on cellular Ca(2+) mobilization. RESULTS: The resting cellular calcium concentration of cultured SO cell was 108+/-21 nmol x L(-1).The intracellular Ca2+ increases induced by 20 mmol x L(-1) KCl, 10(-7) mol x L(-1) ACh and 10(-7) mol x L(-1) CCK were 183+/-56% 161+/-52% and 130+/-43%, respectively. When the extracellular Ca2+ was eliminated by 2 mmol x L(-1) EGTA and 5 micromol x L(-1) verapamil, the intracellular Ca2+ increases induced by KCl, ACh and CCK were 20+/-14%,82+/-21% and 104+/-23%, respectively. After the preincubation with heparin, the Ca2+ increases were 62+/-23% and 23+/-19% induced by ACh and CCK, as for preincubation with procaine they were 72+/-28% and 85+/-37% induced by ACh and CCK, respectively. Pretreatment with CL for 18 h, the resting cellular Ca2+ concentration elevated to 152+/-26 nmol x L(-1), however, the cellular Ca2+ increase percentages in response to these agonists were 67+/-32%,56+/-33% and 34+/-15%. CONCLUSION: KCl elicit the SO cellular Ca2+ increase depends on influx of extracellular Ca2+, ACh evoked the SO cellular Ca2+ increase is through the mobilization of intracellular Ca2+ pool and influx of extracellular Ca2+ as well, CCK excites the SO cells mainly through mobilization of intracellular IP3-sensitive Ca2+ store. After the incorporation with cholesterol liposome, KCl,ACh and CCK induced cellular Ca2+ increase percentages decreased.