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Biomedical subjects

M Prieto

Publications and source records attributed to M Prieto.

At least 55 records · Page 3Linked to original sources
PubMed2001

De novo hepatitis B after liver transplantation from hepatitis B core antibody-positive donors in an area with high prevalence of anti-HBc positivity in the donor population.

Transmission of hepatitis B virus (HBV) infection from donors who are negative for hepatitis B surface antigen (HBsAg-) but positive for antibody to hepatitis B core antigen (anti-HBc+) has been reported. However, previous studies were generally performed in geographic regions with a low prevalence of anti-HBc positivity in the liver donor population. The aims of this study are (1) to assess the risk for de novo hepatitis B in recipients of livers from anti-HBc+ donors in an area of high prevalence of anti-HBc positivity in the donor population, and (2) to analyze the risk factors for acquisition of HBV infection from anti-HBc+ donors. The transplantation experience of a single center between 1995 and 1998 was reviewed. Thirty-three of 268 liver donors (12%) were HBsAg- and anti-HBc+ during the study period. The proportion of anti-HBc+ donors increased with age; it was lowest (3.6%) in donors aged 1 to 20 years and highest (27.1%) in donors aged older than 60 years. Of the 211 HBsAg- recipients with 3 months or more of HBV serological follow-up, 30 received a liver from an anti-HBc+ donor and 181 received a liver from an anti-HBc- donor. Hepatitis B developed in 15 of 30 recipients (50%) of livers from anti-HBc+ donors but in only 3 of 181 recipients (1.7%) of livers from anti-HBc- donors (P < .0001). None of the 4 recipients who were antibody to HBsAg (anti-HBs)+ at the time of transplantation developed HBV infection after receiving a liver from an anti-HBc+ donor compared with 15 of 26 recipients (58%) who were anti-HBs- (P =.10). None of the 5 anti-HBc+ recipients developed hepatitis B compared with 15 of 25 anti-HBc- recipients (60%; P = 0.04). Child-Pugh score was significantly higher in recipients of livers from anti-HBc+ donors who developed HBV infection than in those who did not (9 +/- 2 v 7 +/- 1; P =.03). In our area, testing liver donors for anti-HBc is mandatory, particularly in older donors. With such information available, anti-HBc+ donors can be safely directed to appropriate recipients, mainly those with anti-HBs and/or anti-HBc at the time of transplantation. In the current era of donor shortage, this policy would allow adequate use of such donors.

Adolescent↗
PubMed2001

Liver transplantation in patients with portal vein thrombosis.

The aim of this study is to analyze the incidence, risk factors, management, and follow-up of patients with portal vein thrombosis (PVT) undergoing primary orthotopic liver transplantation (OLT). Four hundred fifteen OLTs were performed in 391 patients. In 62 patients, partial (group 1; n = 48) or complete (group 2; n = 14) PVT was found at the time of surgery. Portal flow was reestablished by venous thrombectomy. In this study, we compare 62 primary OLTs performed in patients with PVT at the time of OLT with a group of 329 primary OLTs performed in patients without PVT (group 3) and analyze the incidence of PVT, use of diagnostic methods, surgical management, and outcome. We found no significant differences among the 3 groups for length of surgery, cold and warm ischemic times, and postoperative stay in the intensive care unit. With the piggyback technique, groups 1 and 2 had greater blood losses and required more blood transfusions than group 3. The early reoperation rate was greater in group 2. The incidence of rethrombosis was 4.8% (group 1, 2%; group 2, 14.3%). Reexploration and thrombectomy (2 patients) and retransplantation (1 patient) had a 100% mortality rate. In particular, the mortality rate of patients with complete PVT with extension into the splanchnic veins is high (33%). Three-month and 4-year patient survival rates were statistically similar in the 3 groups. The presence of PVT at the time of OLT is not a contraindication for OLT. However, if PVT extends into the splanchnic veins, the outcome is guarded.

Adult↗
PubMed2001

Are posttransplantation protocol liver biopsies useful in the long term?

Controversy exists about the usefulness of yearly protocol liver biopsies after liver transplantation, mainly among patients with normal transaminase levels. The aim of this study is to determine (1) the prevalence and cause of histological liver injury in transplant recipients with a minimum histological follow-up of 1 year (n = 254), and (2) the correlation between histological findings and transaminase values. The main indication for liver transplantation was viral-related cirrhosis (61%; 86% caused by hepatitis C virus [HCV]). Protocol liver biopsies were performed yearly for the first 5 years in HCV-infected transplant recipients and at 1 and 5 years in the remaining patients. Histological liver injury included several categories of liver damage (hepatitis, rejection, steatohepatitis, cholangitis, and Budd-Chiari-like lesions). Among biopsy specimens categorized as hepatitis, severe hepatitis was defined as the presence of stage 3 or greater fibrosis. The prevalence of liver injury increased significantly with time (42% v 56% at 1 and 5 years, respectively; P =.09) and was significantly greater in patients who underwent transplantation for HCV-related cirrhosis than in those who underwent transplantation for other reasons (P =.0001). The most frequent category of liver injury was hepatitis (97% and 96% at 1 and 5 years, respectively). Although a proportion of patients with liver injury (12% to 29%) had normal transaminase values, this percentage was almost null in patients with severe hepatitis. Normal histological characteristics were found in the vast majority of non-HCV-infected transplant recipients with normal transaminase values. Given the high prevalence of abnormal histological findings, particularly the increase over time of those defined as severe, protocol liver biopsies are clearly justified in HCV-infected transplant recipients. Conversely, given the rarity of abnormal histological findings, protocol liver biopsies should be questioned in non-HCV-infected transplant recipients with normal transaminase values.

Adult↗
PubMed2001

Up-regulation of endoglin, a TGF-beta-binding protein, in rats with experimental renal fibrosis induced by renal mass reduction.

BACKGROUND: The central process in chronic renal failure is the progressive accumulation of extracellular matrix in the glomeruli and in the tubulo-interstitial space, resulting in renal fibrosis. Transforming growth factor-beta1 (TGF-beta1) up-regulation plays a major role in the genesis of renal fibrosis. Endoglin is a membrane glycoprotein that binds TGF-beta1 and TGF-beta3 with high affinity. An increased level of endoglin immunostaining has been demonstrated previously in biopsies from patients with chronic progressive renal disease. We have assessed the expression of endoglin in the rat 5/6th renal mass reduction (RMR) model. METHODS: One, 3 and 5 months after RMR, mean arterial pressure and renal function were measured, animals were sacrificed, renal fibrosis was evaluated quantitatively and the expression of endoglin was assessed by western blot, northern blot and immunohistochemistry. RESULTS: RMR induced a progressive increase in mean arterial pressure and urinary protein excretion. Renal corpuscular area, and mesangial and interstitial fibrosis increased with time after RMR. Immunohistochemical staining for endoglin demonstrated its expression mainly on the endothelial surface of major vessels. In kidneys 1 and 3 months after RMR, the expression of endoglin in renal corpuscles was limited to Bowman's parietal epithelium. In rats 5 months after RMR, the immunoexpression in glomerular endothelium was more marked. Northern blot analysis revealed that rats with RMR showed an increase in the expression of mRNA for endoglin, only at 5 months after RMR. Western blot analysis gave a different time course: a marked increase in the first month, a decrease in the 3rd month and a further increase in the 5th month after RMR. CONCLUSIONS: The present study demonstrates increased endoglin expression in rats with severe hypertension and renal damage. This increased endoglin expression coincides with the period of higher renal damage and renal dysfunction.

Animals↗
PubMed2001

Famciclovir treatment in transplant recipients with HBV-related liver disease: disappointing results.

OBJECTIVE: Long-term administration of hepatitis B immune globulin is effective as prophylaxis for hepatitis B virus (HBV) reinfection but is limited by cost, side effects, availability and a failure rate of 20%. Famciclovir has been shown to be effective in the treatment of hepatitis B in the immunocompetent patient. Fewer data exist in the liver transplant setting, particularly regarding its efficacy in de novo HBV infection. The aims of this pilot study were to determine the effectiveness and safety of long-term administration of famciclovir in recurrent (n = 3) and de novo (n = 3) HBV infection after liver transplantation. METHODS: Six patients with postransplant HBV infection (positivity of serum HBsAg and HBV DNA), four of whom were HBeAg positive, were treated with famciclovir (500 mg, 3 times a day) with a minimum follow-up period of 12 months. Biochemical, serological, virological (HBV DNA by hybridization assays and polymerase chain reaction), and histological (including HBV immunostaining) endpoints were evaluated. RESULTS: None of the patients had a complete biochemical response, with a near complete normalization of ALT levels being observed in 3/6 patients. There was a lack of correlation between virological and biochemical responses. None of the patients seroconverted to anti-HBs or anti-HBe. A virological clearance was observed in only two patients, whereas a moderate reduction in HBV DNA levels was present in one. HBV DNA levels were higher than levels during pretreatment in the three remaining patients. Histological improvement was only observed in one patient. CONCLUSION: Famciclovir alone appears of limited efficacy in the treatment of HBV infection after liver transplantation.

2-Aminopurine↗
PubMed2001

Solitary adrenal gland metastasis of a follicular thyroid carcinoma presenting with hyperthyroidism.

Follicular thyroid carcinoma typically manifests under euthyroid conditions, and diagnostic scintigraphy usually identifies a cold nodule. Sometimes, such tumors can appear in the context of hyperthyroidism, which can be caused by a toxic multinodular goitre, a toxic adenoma, or even carcinoma. We report a case of follicular thyroid carcinoma discovered after surgical treatment of a toxic multinodular goiter, in which solitary adrenal gland metastasis was detected five years later. A (131)I whole body scan is the diagnostic method of choice for functioning thyroid metastasis.

Adenocarcinoma, Follicular↗
PubMed2001

Donor scoring system for cadaveric renal transplantation.

We studied early renal function in 241 consecutive patients who received cadaveric renal transplants at two different transplantation centers (group 1, n = 90; group 2, n = 151). Univariate and multivariate analyses of data from group 1 showed a significant correlation between seven donor variables and early renal function after cadaveric renal transplantation. A scoring system was developed from these seven donor variables (cause of death, 0-6 points; history of hypertension, 0-6; final creatinine clearance before procurement, 0-6; age, 0-6; history of diabetes mellitus, 0-3; cold ischemia time, 0-3; and severity of renal artery plaque, 0-3). Data from group 2 were used to validate the donor scoring system and stratify cadaver kidneys on the basis of score: grade A, 0-5 points; grade B, 6-10; grade C, 11-15; and grade D, 16-32. A significant decline in early renal function was observed with increasing donor score and grade of cadaver kidney. In conclusion, a donor scoring system based on information available at the time of procurement can be used to estimate early graft function after cadaveric renal transplantation and may assist in the allocation of marginal organs.

Adolescent↗
PubMed2000

A fluorescence study of the interaction and location of (+)-totarol, a diterpenoid bioactive molecule, in model membranes.

(+)-Totarol, a diterpene extracted from Podocarpus totara, has been reported as a potent antioxidant and antibacterial agent. Although the molecular mechanism of action of this hydrophobic molecule remains unknown, recent work made in our laboratory strongly suggests that it could be lipid-mediated. Since (+)-totarol contains a phenolic ring, we have studied the intrinsic fluorescent properties of this molecule, i.e., quantum yield, lifetime, steady-state anisotropy and emission spectra, both in aqueous and in phospholipid phases, in order to obtain information on the interaction and location of (+)-totarol in biomembrane model systems. The phospholipid/water partition coefficient of (+)-totarol was found to be very high (K(p)=1.8x10(4)), suggesting that it incorporates very efficiently into membranes. In order to estimate the transverse location (degree of penetration) of the molecule in the fluid phase of DMPC model membranes, the spin labelled fatty acids 5-NS and 16-NS were used in differential quenching experiments. The results obtained show that (+)-totarol is located in the inner region of the membrane, far away from the phospholipid/water interface. Since (+)-totarol protects against oxidative stress, its interaction with an unsaturated fatty acid, trans-parinaric acid, was studied using fluorescence resonance energy transfer. No significant interactions were observed, molecules of trans-parinaric acid distributing themselves randomly amongst those of (+)-totarol in the phospholipid membrane.

Abietanes↗
PubMed2000

Topography of nicotinic acetylcholine receptor membrane-embedded domains.

The topography of nicotinic acetylcholine receptor (AChR) membrane-embedded domains and the relative affinity of lipids for these protein regions were studied using fluorescence methods. Intact Torpedo californica AChR protein and transmembrane peptides were derivatized with N-(1-pyrenyl)maleimide (PM), purified, and reconstituted into asolectin liposomes. Fluorescence mapped to proteolytic fragments consistent with PM labeling of cysteine residues in alphaM1, alphaM4, gammaM1, and gammaM4. The topography of the pyrene-labeled Cys residues with respect to the membrane and the apparent affinity for representative lipids were determined by differential fluorescence quenching with spin-labeled derivatives of fatty acids, phosphatidylcholine, and the steroids cholestane and androstane. Different spin label lipid analogs exhibit different selectivity for the whole AChR protein and its transmembrane domains. In all cases labeled residues were found to lie in a shallow position. For M4 segments, this is compatible with a linear alpha-helical structure, but not so for M1, for which "classical" models locate Cys residues at the center of the hydrophobic stretch. The transmembrane topography of M1 can be rationalized on the basis of the presence of a substantial amount of non-helical structure, and/or of kinks attributable to the occurrence of the evolutionarily conserved proline residues. The latter is a striking feature of M1 in the AChR and all members of the rapid ligand-gated ion channel superfamily.

Amino Acid Sequence↗
PubMed2000

Partition of membrane probes in a gel/fluid two-component lipid system: a fluorescence resonance energy transfer study.

A non-ideal lipid binary mixture (dilauroylphosphatidylcholine/distearoylphosphatidylcholine), which exhibits gel/fluid phase coexistence for wide temperature and composition ranges, was studied using photophysical techniques, namely fluorescence anisotropy, lifetime and resonance energy transfer (FRET) measurements. The FRET donor, N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)-dilauroylphosphatidylethanol amine, and a short-tailed FRET acceptor, 1,1'-didodecil-3,3,3',3'-tetramethylindocarbocyanine (DiIC12(3)), were shown to prefer the fluid phase by both intrinsic anisotropy, lifetime and FRET measurements, in agreement with published reports. The other studied FRET acceptor, long-tailed probe 1,1'-dioctadecil-3,3,3',3'-tetramethylindocarbocyanine (DiIC18(3)), is usually reported in the literature as partitioning mainly to the gel. While intrinsic lifetime studies indeed indicated preferential partition of DiIC18(3) into a rigidified environment, FRET analysis pointed to an increased donor-acceptor proximity as a consequence of phase separation. These apparently conflicting results were rationalized on the basis of segregation of DiIC18(3) to the gel/fluid interphase. In order to fluid-located donors sense these interphase-located acceptors, fluid domains should be small (not exceed approximately 10-15 nm). It is concluded that membrane probes which apparently prefer the gel phase may indeed show a non-random distribution in this medium, and tend to locate in an environment which simultaneously leads to less strict packing constraints and to favorable hydrophobic matching interactions.

4-Chloro-7-nitrobenzofurazan↗
PubMed2000

[Frozen section biopsy in the assessment of organs for transplantation].

BACKGROUND: The success of transplantation and the increase in its indications has caused organ donations to be unable to meet the global demand. By broadening the donor selection criteria and accepting so-called suboptimal donors in an attempt to solve this problem, a careful individualized assessment is required of the validity of each donor. This often implies the need for a pretransplantation biopsy study. MATERIAL AND METHODS: Evaluation of frozen-section biopsy studies in the assessment of graft and donor validness in the the transplantation program of the La Fe University Hospital (Valencia, Spain) during 1998, when a total of 301 solid organ transplantations were performed. RESULTS: Sixty pretransplantation frozen-section biopsies were performed (29 of the liver, 21 renal, 3 lymph nodes, 3 brain, 2 prostatic, 1 myometrial and 1 pericardial). As a result of the bioptic study, 18 transplantations were invalidated (30% of all biopsies). The most frequent causes of invalidation were liver macroesteatosis (7 cases), malignancies (5 cases) and renal parenchymal lesions (5 cases). Among the tumor diagnosis there were one false-positive and one false-negative results of malignancy. CONCLUSION: Frozen-section biopsies evaluation in suboptimal organ donors or donors suspected of suffering disease integrates morphological analysis in the transplantation team decision process, and affords a quality factor in the selection of donors.

Adolescent↗
PubMed2000

Tanycytes transplanted into the adult rat spinal cord support the regeneration of lesioned axons.

During past years a number of therapeutic strategies have been developed in order to stimulate axonal regeneration after traumatic injuries of the spinal cord. Recently, encouraging data have been obtained by grafting specific glial cells such as Schwann cells or olfactory ensheathing glial cells, known to support the regeneration of peripheral or central axons, respectively. In a recent series of studies, we have shown that tanycytes, a particular glial cell type present in the mediobasal hypothalamus, were able to support the regeneration of a variety of axons innervating this region. The aim of the present study was to determine whether tanycytes could also support the regeneration of lesioned spinal axons. Cultured hypothalamic tanycytes and cortical astrocytes were prelabeled with Fast blue (FB) and grafted into the thoracic spinal cord of adult rats. Three weeks after the transplantation, the animals were fixed and spinal cord sections treated for multiple fluorescence detection of the FB-labeled transplanted cells on the one hand and of various glial and neuronal markers on the other hand. We show here that in all the spinal cords examined, transplanted tanycytes or astrocytes formed large spherical clusters of about 0.5 mm in diameter, located in the mediolateral spinal cord layer. The immunodetection of glial markers showed that transplanted astrocytes exhibited intense immunostaining for both glial fibrillary acidic protein (GFAP) and vimentin (VIM), whereas transplanted tanycytes were intensely immunostained for VIM, but GFAP negative. The immunodetection of axonal markers showed that contrasting with astrocyte transplants, tanycyte transplants were invaded by numerous axonal fibers. These data indicate that tanycyte transplants may represent a useful therapeutic tool for the reparation of the lesioned spinal axons.

Age Factors↗
PubMed2000

Modification of plasma membrane lipid order and H+-ATPase activity as part of the response of Saccharomyces cerevisiae to cultivation under mild and high copper stress.

Plasma membrane lipid disorganization takes place in cells of Saccharomyces cerevisiae grown under copper stress, as shown by fluorescence anisotropy measurements with the lipid reporter probe 1,6-diphenyl-1,3,5-hexatriene. The extent of plasma membrane disorganization, presumably due to copper-induced lipid peroxidation, was discontinuous when measured in cells grown in media supplemented with different concentrations of CuSO4. Results suggested the existence of adaptive mechanisms that cells employ to protect themselves against the deleterious effects of copper. The adaptive mechanisms examined in this study included the coordinate increase in the activities of Cu,Zn-superoxide dismutase (up to five-fold), glutathione reductase (up to 1.7-fold), and plasma membrane H+-ATPase (up to three-fold). These enzyme activities showed maximal levels in cells grown with copper supplied at intermediate concentrations, within the range that allowed growth. Significantly, at these concentrations, plasma membrane disorganization did not increase when increasing amounts of CuSO4 were supplied. However, at copper concentrations close to the maximal that allowed growth, the capacity of the yeast cell response to cope with the deleterious effects of copper was exceeded; plasma membrane lipid organization and plasma-membrane-bound H+-ATPase activity drastically declined in response to the increased levels of copper stress and the consequences on growth kinetics were even more severe. Our results clearly suggest that modification of plasma membrane H+-ATPase activity is either part of or the result of the global response of yeast to mild or high copper stress.

Cell Membrane↗
PubMed2000

HCV-related fibrosis progression following liver transplantation: increase in recent years.

BACKGROUND/AIMS: The natural history and predictors of HCV-related disease severity post-transplantation are uncertain. The aims of this study were to define the natural history of post-transplantation HCV infection by assessing the rate of fibrosis progression, to determine if the post-transplantation natural history differs from that observed pre-transplantation, and to identify predictors of post-transplantation disease progression. METHODS: Post-transplantation biopsies (mean: 3+/-1.6/patient) from 284 patients were scored according to histologic stage, using the method of Desmet et al. Change in fibrosis score (fibrosis progression/year) post-transplantation was used as the primary outcome. Predictors analyzed included viral factors (genotype and viral load at transplantation), patient demographics, year of transplantation, country of transplantation, pre-transplantation fibrosis progression, immunosuppression and laboratory data. RESULTS: There was a linear association between change in fibrosis score and time from transplantation, with a median rate of fibrosis progression per year of 0.3 (0.004-2.19/year). Using parametric time-to-event analysis, the expected median duration to cirrhosis was 10 years. The rate of post-transplantation fibrosis progression was significantly higher than pre-transplantation (0.2/year (0.09-0.8) p<0.0001), and higher in Spanish than US centers (0.48 (0.01-2.19) vs 0.28 (0.004-2.08); p=0.09) despite similar progression rates prior to transplantation. Variables independently associated with post-transplantation progression included year of transplantation (p=0.0001), race (p=0.02), number of methyl-prednisolone boluses (p=0.03), and HCV RNA levels at transplantation (p=0.01). CONCLUSIONS: HCV-related disease progression is accelerated in immunocompromised compared to immunocompetent patients, with a progressive increase in patients who have recently undergone liver transplantation. Changes in patient management post-transplantation over time and between transplant centers may account for the increase in fibrosis progression observed in recent years.

Adult↗
PubMed2000

Natural history of clinically compensated hepatitis C virus-related graft cirrhosis after liver transplantation.

The natural history of clinically compensated hepatitis C virus (HCV) cirrhosis after liver transplantation is unknown. This information is relevant to transplant centers to improve the management of these patients and decide the optimal timing for retransplantation. The aims of the study were (1) to describe the natural history of patients with HCV-cirrhosis transplants in a center with annual liver biopsies, and (2) to determine predictors for clinical decompensation, retransplantation, and mortality rates. A total of 49 patients with HCV-graft cirrhosis, 39 clinically compensated at histologic diagnosis of cirrhosis (post-liver transplantation cirrhosis) were included and followed up for 1 year (15 days-3.5 years). All patients tested were infected with genotype 1b. Predictive variables included histologic activity index (HAI) at post-liver transplantation cirrhosis, liver function tests, age, sex, and maintenance immunosuppression. Eighteen of 39 patients developed at least 1 episode of decompensation after a median of 7.8 months (4 days-2.6 years; 93% ascites). The cumulative probability of decompensation was 8%, 17%, and 42% at 1, 6, and 12 months, respectively. Graft and patient survival rates were 100%, 85%, and 71% and 100%, 92%, and 74% at 1, 6, and 12 months, respectively. Patient survival rates dropped significantly once decompensation developed (93%, 61%, and 41% at 1, 6, and 12 months, respectively). Variables associated with decompensation, retransplantation, and mortality rate included a high Child-Pugh score (>A), low levels of albumin at post-liver transplantation cirrhosis, and a short interval between liver transplantation and post-liver transplantation cirrhosis. The natural history of clinically compensated HCV-graft cirrhosis is shortened when compared with immunocompetent patients. If retransplantation is considered, it should be performed promptly once decompensation develops.

Adult↗
PubMed2000

Pancreas transplantation for the prevention of diabetic nephropathy.

Diabetic nephropathy is the leading cause of kidney failure in the United States. Poor glycemic control, hypertension, and smoking have been implicated as risk factors for the development and progression of diabetic nephropathy in patients with type 1 diabetes mellitus. Improved medical therapy including angiotensin-converting enzyme inhibitors and tight glycemic control with use of intensive insulin therapy have been shown to reduce the progression of diabetic nephropathy substantially based on albumin excretion rates. Despite these improvements in medical management, many patients still experience progression from early diabetic nephropathy to end-stage renal disease. Successful pancreas transplantation leads to normal glycemic control in patients with type 1 diabetes, but historically it has generally been limited to patients with both kidney failure and diabetes. In this review of the current treatment of diabetic nephropathy, we examine the potential role of preemptive pancreas transplantation in patients with diabetic nephropathy.

Albuminuria↗
PubMed1999

The pentaene macrolide antibiotic filipin prefers more rigid DPPC bilayers: a fluorescence pressure dependence study.

Filipin is a pentaene macrolide antibiotic which was previously shown to incorporate more extensively into DPPC bilayers below the main phase transition temperature than above this temperature. This result was extremely unusual because drugs tend to be expelled from ordered gel phases. However, such results could not be safely attributed to the phase change of the bilayer itself because the temperature was changing concomitantly. In this work we changed the bilayer phase isothermally (53 degrees C) by hydrostatic pressure variation and discovered that filipin has a slightly more extensive incorporation in the pure DPPC gel phase (P>ca. 54.4 MPa): Kp,lc approximately 3x10(3) vs. Kp,gel approximately 6x10(3). The presence of sterols (45% molar ergosterol or cholesterol) caused an increase in the partition coefficients, regardless of pressure, ergosterol having a more pronounced effect (Kp approximately 2x10(4)-6x10(4)). Kp was pressure dependent in both cases, but mainly with cholesterol (Kp approximately 2x10(3)-2x10(4)). At variance with cholesterol, when ergosterol was used, no phase transition was detected. This difference cannot be due to a more extended uptake of filipin by cholesterol-containing membranes, and so must be due to specific interactions with cholesterol. In agreement with this finding, we discovered that filipin is more tightly packed (lower partial molar volume) in the cholesterol-rich phase than in the ergosterol-rich phase. Our results also point to a 2:1 DPPC:cholesterol stoichiometry in the cholesterol-rich phase (17% molar cholesterol). All partition coefficients were calculated from steady-state fluorescence anisotropy measurements.

1,2-Dipalmitoylphosphatidylcholine↗