Probing diffusion laws within cellular membranes by Z-scan fluorescence correlation spectroscopy

The plasma membrane of various mammalian cell types is heterogeneous in structure and may contain microdomains, which can impose constraints on the lateral diffusion of its constituents. Fluorescence correlation spectroscopy (FCS) can be used to investigate the dynamic properties of the plasma membrane of living cells. Very recently, Wawrezinieck et al. (Wawrezinieck, L., H. Rigneault, D. Marguet, and P. F. Lenne. 2005. Biophys. J. 89:4029-4042) described a method to probe the nature of the lateral microheterogeneities of the membrane by varying the beam size in the FCS instrument. The dependence of the width of the autocorrelation function at half-maximum, i.e., the diffusion time, on the transverse area of the confocal volume gives information on the nature of the imposed confinement. We describe an alternative approach that yields essentially the same information, and can readily be applied on commercial FCS instruments by measuring the diffusion time and the particle number at various relative positions of the cell membrane with respect to the waist of the laser beam, i.e., by performing a Z-scan.     

Rat-liver cholesterol 7 alpha-hydroxylase. 1. Development of a new assay based on the enzymic exchange of the tritium located on the 7 alpha position of the substrate.

A new assay is described to measure the activity of cholesterol 7alpha-hydroxylase and compared to the conventional 14C method used by other investigators. This method is based on the mechanism of the enzymic hydroxylation, i.e. a direct and stereospecific substitution of the 7alpha-hydrogen by a hydroxyl group. [7alpha-3H]Cholesterol is incubated at 37 degrees C and in the presence of molecular O2, in a medium buffered by postassium phosphate at pH 7.4 and containing liver microsomes (or 9000 X g supernatant), NADPH, MgCl2 and cysteamine. Tween-80 (1.5 mg/ml) is used to introduce enough substrate (300 muM) in the incubation mixture to saturate the enzyme (Km = 100 muM). Under these conditions the tritiated water released into the incubation medium reflects accurately the enzymic activity. The results obtained with this method are similar to the one obtained with a [4-14C]cholesterol technique (r = 0.96; P less than 0.001). The main advantage of the [7alpha-3H]cholesterol method is a complete independence from further metabolism of the first enzymic product, the 7alpha-hydroxycholesterol, the tritiated water representing the entire cholesterol 7alpha-hydroxylase activity.     

Rat-liver cholesterol 7alpha-hydroxylase. 3. New results about its circadian rhythm.

The establishement of the circadian rhythm of cholesterol 7alpha-hydroxylase activity requires protein and RNA synthesis. The spontaneous decrease of the enzymic activity, at the end of the night, allows us to evaluate a half-life time of about two hours. The half-life time goes up to about four hours when the enzymatic activity decay is measured following cycloheximide administration. This difference suggests that an active mechanism is involved in the control of the enzyme degradation. The daily variation of the enzyme activity is regulated via the hypothalamo-hypophysis-adrenal axis. At the cellular level glucocorticoids are the most likely responsible agent. The hepatic cholesterol 7alpha-hydroxylase variations always parallel the plasmatic corticosterone concentration fluctuations, the latter being by far the most important adrenocortical excretion product. These two rhythms are modified in a similar manner under different physio-pathological conditions, such as the inversion of lighting in the animal room or the inversion of feeding time. Of these two parameters, the moment of food intake is the most important and accounts for the synchronisation of the rhythm in the animals. The rhythm is retained after several days of starvation but its amplitude decreases and the individual variations among the animals increase significantly at each time point.     

Microsurgical vasectomy reversal: results and predictors of success

Microsurgical vasectomy reversal is a challenge for the physician but successful treatment depends on the experience and skills of the surgeon. Fertility can often be restored, thus avoiding the need for artificial reproductive techniques. Also, the surgical procedures can be combined with sperm aspiration and cryopreservation, to be used for Intracytoplasmic sperm injection (ICSI) in cases of surgical failure. We describe the results of 217 vasovasostomy procedures, with special emphasis on recent technical refinements and prognostic indicators. Between 1998 and 2002 we performed 217 vasovasostomy-procedures in an outpatient clinic setting. Refertilisation was successful in 76.5%, spontaneous pregnancy occurred in 42% of the couples after, a follow-up of at least 1 year. The main prognostic factors determining the outcome of the surgery was the interval between vasectomy and refertilisation and the age of the female partner: patency was 89% after an interval of less than 5 years and pregnancy occurred in 56% of these couples. After an interval of more than 10 years patency decreased to 75% and pregnancy results dropped to 24%. Epididymal dysfunction with poor motility score and secondary epididymal obstruction appeared to be common after a long interval. Furthermore, in men with partners older than 35 years of age pregnancy was only 21%, indicating limited ovarian reserve as an important factor in determining the final outcome. In men with a long obstructive interval between vasectomy and reversal an obstruction of the epididymis can be found due to a blow-out of the epididymal tubule with subsequent leakage of semen in the organ and fibrosis. A vaso-epididymostomy procedure is needed to treat the obstruction. Recently, surgical refinements, such as the invagination technique, have been introduced for the vaso-epididymostomy procedure, showing promising first results. This simplified technique enables less experienced microsurgeons to perform this difficult operation successfully. The results of vasectomy reversal procedures can be improved substantially if the surgeon is able to perform a vaso-epididymostomy in cases of a secondary epididymal obstruction, occurring in about 25% of men with an interval of more than 10 years.     

Comparison of aryl hydrocarbon hydroxylase and epoxide hydratase. Induction in primary fetal rat liver cell culture

The activity of aryl hydrocarbon hydroxylase (AHH) and/or epoxide hydratase (EH) is induced in primary fetal rat liver cell culture by benz-[alpha]anthracene (BA), phenobarbital (PB), cigarette smoke condensate (CSC), 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and trans-stilbene oxide (TSO). The response of the two enzymes to the different chemicals varies as follows: (a) AHH is induced by lower concentrations of BA, PB and CSC than those required to significantly induce EH; (b) AHH is selectively induced by TCDD and by low BA concentrations; (c) the kinetics of AHH induction by BA, PB and CSC is faster than that of EH; (d) TSO is a selective inducer of EH. As described earlier for AHH, RNA and protein synthesis and the continuous presence of the inducer are required in the early phases of EH induction. Later when the EH activity has reached a plateau, intact RNA and protein synthesis is not necessary to maintain the enzyme at its optimal value. The removal of the inducer determines a decay of the EH activity, allowing the estimation of a biological tau 1/2 of about 72 h. TSO prevents the AHH induction by PB, but not that mediated by BA and CSC. Added together with PB, BA, CSC or PB plus BA, TSO induces the EH activity in a more than additive manner. This effect is only seen after 6 days of continuous treatment. These results indicate that in this tissue culture model, the mechanism of AHH and EH induction can clearly be dissociated.     

Synthesis of the fragments A1-,, A9-15 and A16-21 of ovine insulin A chain using the S-tert-butylmercapto residue for thiol protection (author's transl)

The following paper describes the synthesis of the fragments A1-8, A9-15 and A16-21 of the ovine insulin A chain using the S-tert-butylmercapto residue for thiol protection. The synthesized fragments, which showed a good solubility in organic solvents, were partially deprotected with trifluoracetic acid and converted to the corresponding S-sulfonates quantitatively by oxidative sulfitolyses at pH 7.6.