Anionic phospholipids decrease the rate of slippage on the Ca(2+)-ATPase of sarcoplasmic reticulum.

Accumulation of Ca(2+) by the Ca(2+)-ATPase of skeletal-muscle sarcoplasmic reticulum has been measured in reconstituted, sealed vesicles as a function of lipid composition. Measurements were performed in the presence of carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP) to eliminate any effects of H(+) transport; in the presence of FCCP, addition of valinomycin had no effect on the level or rate of accumulation of Ca(2+) showing that, in the presence of FCCP, no electrical potential built up across the membrane. Levels of accumulation were low when the phospholipid was dioleoylphosphatidylcholine (DOPC), even though DOPC supports high ATPase activity. Inclusion of 10 mol% anionic phospholipid [dioleoylphosphatidic acid (DOPA) or dioleoylphosphatidylserine (DOPS)] led to higher levels of accumulation of Ca(2+), 10 mol% being the optimum concentration. Cardiolipin or phosphatidylinositol 4-phosphate were more effective than DOPA or DOPS in increasing accumulation of Ca(2+). Effects of anionic phospholipids were seen in the presence of an ATP-regenerating system to remove ADP, and in the presence of phosphate within the reconstituted vesicles to precipitate calcium phosphate. Rates of passive leak of Ca(2+) from the reconstituted vesicles were slow. The Ca(2+)-accumulation process was simulated assuming either simple passive leak of Ca(2+) from the vesicles or assuming slippage on the ATPase, a process in which the phosphorylated intermediate of the ATPase releases bound Ca(2+) on the cytoplasmic rather than the lumenal side of the membrane. The experimental data fitted to a slippage model, with anionic phospholipids decreasing the rate of slippage.

A randomised controlled trial to evaluate the effects of flumazenil after midazolam premedication in outpatients undergoing colonoscopy.

The degree of sedation and amnesia, subjective assessment of awakening and side effects after intravenous injection of 3-4 mg midazolam and 1 mg flumazenil or placebo were studied directly after colonoscopy, and on the first and the eight day. A total of 91 patients were studied; 45 patients were given flumazenil and 46 patients a placebo. Five minutes after injection of the test drugs all 45 patients given flumazenil but only 38 patients given the placebo were alert (p = 0.006). All three response criteria (for sedation, amnesia and subjective assessment of awakening) were fulfilled by 84.4% of the patients given flumazenil and 45.7% of the patients given the placebo (p = 0.0002). Thirty minutes after injection of the test drugs dizziness, nausea, and fatigue were found in 3 patients given flumazenil and in 10 patients given placebo. One day after colonoscopy 9 of 45 patients (20%) given midazolam and flumazenil complained of fatigue and 9 of 46 patients (19.5%) given midazolam and placebo. Eight days (+/- 1 day) later two patients in each group complained of headache, nausea and fatigue. No patient developed phlebitis at the injection site. Flumazenil seems to be a safe and efficient drug for reversing the sedative effect of midazolam, premedication after colonoscopy. However, resedation due to the effects of midazolam may occur. Flumazenil thus permits administration of a higher dose of midazolam without prolongation of the surveillance time. Improved exploitation of time, space and nursing resources is thus possible without jeopardizing patient safety, although caution is necessary since patients may not be fit to resume all normal activities.