Evaluation of the prognostic and predictive value of p53 and Bcl-2 in breast cancer patients participating in a randomized study with dose-dense sequential adjuvant chemotherapy

PURPOSE

To assess the prognostic and predictive significance of p53 and Bcl-2 protein expression in high risk patients with breast cancer treated with dose-dense sequential chemotherapy.

PATIENTS AND METHODS

From June 1997 until November 2000, 595 patients were randomized to three cycles of epirubicin (E) 110 mg/m2 followed by three cycles of paclitaxel (P) 250 mg/m2 followed by three cycles of 'intensified' CMF (cyclophosphamide 840 mg/m2, methotrexate 47 mg/m2 and fluorouracil 840 mg/m2) or to four cycles of E, followed by four cycles of CMF. p53 and Bcl-2 expression was investigated by immunohistochemistry in 392 and 397 patients respectively.

RESULTS

Positive expression of p53 was detected in 104 (26.5%) patients and was significantly associated with negative hormonal status, worse histologic grade, higher incidence of disease relapse and higher rate of death. p53 positive expression was a significant negative predictor of overall survival (OS) (P = 0.002) and disease-free survival (DFS) (P = 0.001). Negative expression of Bcl-2 was detected in 203 (51%) patients and was significantly associated with negative hormonal status. Multivariate analysis revealed that, positive p53 expression, higher number of positive nodes and worse tumor grade were related to significantly poorer OS and DFS.

CONCLUSIONS

For both treatments, p53 positive expression was a significant negative prognostic factor for OS and DFS while Bcl-2 was not. No predictive ability of p53 status or Bcl-2 status for paclitaxel treatment was evident.

Hand-assisted Laparoscopic Surgery with a Pfannenstiel Incision in β-Thalassemia Patients: Initial Experience

INTRODUCTION

beta-Thalassemia patients have splenomegaly significant enough to require splenectomy; furthermore, these patients also often require concurrent procedures.

METHODS

Between January and October 2005, seven patients with beta-thalassemia underwent hand-assisted laparoscopic splenectomy with cholecystectomy, appendectomy, and liver biopsy with the hand-port device introduced through a Pfannenstiel incision.

RESULTS

The median age of the patients was 28 years, and the median spleen length was 23 cm. The median operating time was 210 minutes; there were no conversions to an open procedure; and the median spleen weight was 1072 g. One major postoperative complication occurred. The median hospital stay was 6 days.

CONCLUSIONS

The proposed hand-assisted laparoscopic approach is safe and feasible. It provides a minimally invasive alternative that may become the treatment of choice in beta-thalassemia patients who require concurrent operations.

The use of artificial skin in plastic surgery and burns

The use of artificial skin restores the depth and the elasticity of the skin, through restoration of the dermis, with no significant morbidity. Thus we have permanent release of contractures and a pleasing contour with satisfactory functional and cosmetic results. Still, these advantages must be weighed against the necessity for meticulous surgical technique and intensive post-operative care, the waiting period and the cost of the product.

Molecular analysis of GISTs: evaluation of sequencing and dHPLC

Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal tumors of the gastrointestinal tract and are characterized by mutations in the proto-oncogene KIT (c-kit). To date, the detection of genomic alterations of the c-kit gene has been based mostly on direct sequencing. However, sequencing is an expensive and time-consuming approach. Since the technology of WAVE DNA Fragment Analysis System (Transgenomic, Inc., Worcester, MA) (dHPLC) is available in our laboratory, we decided to evaluate its use. Sixteen patients with small/large intestine, stomach tumors were included in the study. Immunohistochemical evaluation was performed on formalin-fixed, paraffin-embedded specimens with the polyclonal antibody CD117 for the KIT protein. After DNA extraction and isolation from paraffin-embedded sections, a nested PCR approach was applied to amplify sequences of exon 11 of the c-kit gene. dHPLC and the ABI Prism 310 Genetic Analyzer (Applied Biosystems, Bedford, MA) were used respectively for screening and identification of genomic alterations. Immunohistochemical analysis revealed strong and diffuse KIT expression in each of the 16 paraffin-embedded sections examined. dHPLC analysis in two temperatures showed the presence of genomic alterations in 8 out of 16 (50%) samples examined. Subsequently, sequence analysis of exon 11 in those samples revealed c-kit alterations in only 8 out of 16 (50%) samples. These were five deletions, one of which was an in-frame deletion one-point mutation and one insertion. Furthermore, the sensitivity of both methods was compared by using different mixtures of a wild-type and a sample with a deletion in exon 11. dHPLC was shown to be able to detect genomic alterations in all four different sample mixtures, whereas with sequence analysis genomic alterations were detected only in the 1:2 and 1:4 sample mixtures. In conclusion, we showed that dHPLC is an efficient and accurate, as well as a more sensitive, method for screening of genomic alterations in exon 11 of the c-kit gene, compared to sequence analysis.

Treatment of non-small cell lung cancer with gefitinib (???Iressa???, ZD1839): the Greek experience with a compassionate-use program

This is a retrospective analysis of 150 patients with advanced non-small cell lung cancer who had failed prior treatment or were unfit for chemotherapy and were treated with oral gefitinib ('Iressa', ZD1839; AstraZeneca) 250 mg/day. Thirty-two patients who received gefitinib for 3 weeks or less were not included in the analysis. For the remaining 118 evaluable patients, the mean age was 63.1 years; most patients had received prior chemotherapy (97.5%), Eastern Cooperative Oncology Group performance status scores 0-2 (97.4%) and stage IV disease (64.4%). The majority were symptomatic (84.6%). Disease control was observed in 30 patients (25.4%), of whom five had a partial response and 25 had stable disease; 18 (15.3%) were not evaluable. Median duration of treatment was 29.9 weeks in responding patients and 11.5 in patients with progressive disease (p<0.0001). Median overall survival was 7.3 months (15.2 months for disease control) and median progression-free survival was 3.2 months. Gefitinib was well tolerated, with grade 3/4 skin rash and diarrhea seen in 2.5 and 4.2% of patients, respectively. Clinical benefit was evaluated using questionnaires before and following treatment with gefitinib. In 82 patients with completed questionnaires, evaluation revealed symptom improvement in 40.1% and improvement in general feeling in 31.4%. Epidermal growth factor receptor (EGFR) analysis found that efficacy did not correlate with tumor EGFR overexpression. Therefore, in this retrospective analysis, gefitinib treatment provided disease control in 25% of patients who derived significant palliative benefit.

In vitro fertilization as a predictor of fertility from cervical insemination of sheep

The objective of this study was to determine if the quality of frozen-thawed ram semen could be effectively evaluated through in vitro fertilization (IVF) procedures prior to insemination as a means of improving pregnancy rate. In experiment 1, frozen semen from four Belclare rams was assessed using IVF and was used for cervical insemination of ewes (n = 181) in 13 pedigree Belclare flocks. There was a significant association between IVF score (proportion of oocytes cleaved at 48 h post insemination) and non-return rate (P < 0.001). For experiment 2, semen from nine Belclare rams was evaluated by IVF and semen from rams with the highest (n = 3) and lowest (n = 2) IVF scores was used for cervical insemination of ewes (n = 111) under experimental conditions. Differences in pregnancy rates between individual rams did not reach significance. Experiment 3 was designed to determine if differences detected between rams at field level could be accurately identified via IVF evaluation and involved frozen semen from eight Norwegian rams of known field fertility (non-return rates ranged from 45.7 to 73.8%). IVF score did not reflect the differences in field fertility. In the final experiment six of the eight Norwegian rams involved in experiment 3 were selected based on IVF score (three highest and three lowest) and their semen was used for cervical insemination (n = 90 ewes). While significant differences in pregnancy rate were found between individual rams (P < 0.02, range: 12.9-65.8%) they were not associated with IVF score. Ewe breed had a significant effect (P < 0.003) on pregnancy rate in both experiments 2 and 4. In conclusion, there was no evidence from this study that the evaluation of semen quality through IVF provided a useful predictor of pregnancy rate under field conditions. It may be that the IVF procedures as used routinely, which are essentially designed to maximize blastocyst yields rather than for detecting differences in fertilizing ability between batches of sperm, need to be modified.

Self-Inflicted Burns in Athens, Greece: A Six-Year Retrospective Study

Self-inflicted burns represent a major social and medical problem. The aim of this study was to record the epidemiology, mortality and etiology of suicide attempts by burning, in Athens, Greece. Over a 6-year period from April 1997 to April 2003, all the medical charts of the patients who were admitted to the Burn Center of the General State Hospital of Athens, Greece, with self-inflicted burns were retrospectively studied. Of the 1435 burn patients, 53 (3.69%) had attempted suicide by self-inflicted burn. Their ages ranged from 18 to 90 years old (mean 53.5 years). Females (57%) outnumbered males (43%). The mean total body surface area (TBSA) burned was 41.6% (range: 15-100%). The overall mortality rate was very high (75.4%). A preexisting psychiatric disorder was present in 43.3% of the patients. In conclusion, the extent and the depth of the burn injuries could explain the high mortality rate seen in these patients, in correlation with their negativism to the treatment. Burn care professionals should be familiar with self-inflicted burn patients who constitute a considerable proportion of major burns and require constant psychiatric support in addition to burn care.

STI571 as a potent inhibitor of growth and invasiveness of human epithelial breast cancer cells

STI571, a specific tyrosine kinase inhibitor, exhibits a substantial therapeutic activity in patients with chronic myeloid leukaemia and gastrointestinal stromal tumors. In this study we examined the activity of STI571 on the growth and invasiveness of three human epithelial breast cancer cell lines of low (MCF-7) and high (ZR-75-1 and MDA-MB-231) invasive potential. Growth of all cell lines in serum-containing medium was significantly inhibited by STI571 in a dose-dependent manner, with an average IC50 of approximately 5-6 microM. Flow cytometric analysis revealed that this effect is characterized by an accumulation of all breast cancer cell types tested in the G2/M-phase of the cell cycle with a concomitant decrease of the percentage of cells in the S-phase. Interestingly, no increase in apoptosis was observed, indicating that the effect of this kinase inhibitor is cytostatic rather than cytotoxic. In addition, STI571 exerts a significant inhibition effect on the invasion of the highly invasive breast cancer cell lines ZR-75-1 and MDA-MB-231. These results encourage further preclinical investigations on the mechanisms underlying the inhibitory effects of STI571, which may be of great value in breast cancer treatment.

Histiocytoid breast carcinoma: a case report of an uncommon histologic variant of lobular carcinoma

A rare case of invasive histiocytoid breast carcinoma is presented. A middle aged female patient underwent quadrantectomy for a palpable mass in her right breast. The neoplastic cells showed pronounced histiocytoid appearance and immunopositivity for cytokeratins 7 and CAM 5,2, EMA, CEA, GCDFP-15, MFG and ER/PR. We report here this uncommon histologic pattern because of the considerable diagnostic interest. Recognition of this histologic variant either in primary or metastatic locations may present some difficulties to the pathologist. Differential diagnostic problems are emphasized and the literature is reviewed.

Embryo survival and recipient pregnancy rates after transfer of fresh or vitrified, in vivo or in vitro produced ovine blastocysts

The aim of this study was to assess the effect of production system and of cryopreservation of ovine embryos on their viability when transferred to recipients. The experimental design was an unbalanced 2 x 2 factorial design of two embryo production systems (in vivo versus in vitro) and two embryo preservation conditions prior to transfer (transferred fresh versus transferred after vitrification/warming). For the production of blastocysts in vivo, crossbred donor ewes (n=30) were synchronised using a 13-day intravaginal progestagen pessary. Ewes received 1500 IU equine chorionic gonadotropin (eCG) 2 days before pessary withdrawal, and were mated 2 days after pessary withdrawal and embryos were recovered surgically (6 days after mating). Blastocysts were produced in vitro (IVP) using standard techniques. Recipients (n=95) were synchronised using a progestagen pessary and received 500 IU eCG at pessary removal and were randomly assigned to receive (two per recipient) in vivo fresh (n=10), in vivo vitrified (n=10), in vitro fresh (n=35) or in vitro vitrified (n=40) blastocysts. Recipients were slaughtered at day 42 of gestation and foetuses recovered. Pregnancy and embryo survival rates were recorded and analysed using CATMOD procedures. Foetal weights and crown-rump lengths were recorded and analysed using generalised linear model (GLM) procedures. There were no statistically significant interactions between the effects of embryo production system and preservation status at transfer on pregnancy rate and embryo survival. The pregnancy rate following transfer of fresh IVP blastocysts was lower (P<0.07) than that of in vivo embryos (54.3% versus 90.0%, respectively). Vitrification resulted in a decrease in pregnancy rate, the effect being more pronounced in the case of IVP embryos (54.3-5.0%, P<0.001) compared with in vivo embryos (90.0-50.0%), although the absolute change was similar (49.3% versus 40.0%). Transfer of fresh IVP blastocysts resulted in a higher proportion of single (78.9% versus 33.3%) and lower proportion of twin (21.1% versus 66.7%) pregnancies than those produced in vivo. This was reflected in a significant difference in embryo survival rate (fresh: 32.8% versus 75.0%, P<0.01; vitrified: 2.5% versus 35.0%, P<0.001, for IVP and in vivo blastocysts, respectively). Similarly, all pregnancies resulting from the transfer of vitrified/warmed IVP blastocysts were single pregnancies, while 40% of those from vitrified/warmed in vivo blastocysts were twin pregnancies; this was reflected in an embryo survival rate of 35.0% versus 75.0%, respectively. There was a significant effect (P=0.0184) of litter size on foetal weight but not on foetal length (P=0.3304). Foetuses derived from the fresh transfer of IVP blastocysts were heavier (6.4+/-0.2g versus 5.8+/-0.2g, respectively, P<0.05) and longer (5.2+/-0.1cm versus 4.8+/-0.1cm, respectively, P<0.01) than those derived from fresh in vivo blastocysts. There was no difference in these parameters as a consequence of vitrification of IVP embryos. However, in vivo blastocysts subjected to vitrification resulted in heavier (6.6+/-0.3g versus 5.8+/-0.2g, respectively, P=0.055) and longer (5.2+/-0.1cm versus 4.8+/-0.1cm, respectively, P<0.05) foetuses than their counterparts transferred fresh.

Current use of HER2 tests

Reliable detection of HER2 overexpression is important for the success of trastuzumab (Herceptin) therapy. Several methods are available for measuring HER2 expression at the DNA, RNA or protein level. The method most frequently employed is immunohistochemical (IHC) detection of the HER2 receptor in paraffin sections. Advantages include the precise localization of the HER2 protein, the availability of paraffin material and the ease of the procedure. However, IHC can be influenced by the sensitivity/specificity of the antibody, tissue treatment and, in particular, subjective assessment. These disadvantages do not exist in the detection of gene amplification by fluorescence in situ hybridization (FISH) or polymerase chain reaction. However, FISH requires expensive equipment that is not widely available in pathology laboratories. Another approach quantitates shed HER2 antigen in the serum by an enzyme-linked immunosorbent assay. The key advantage of this method is the ease of sampling blood, however, serum HER2 concentrations do not accurately reflect the tumor status. Furthermore, this method does not register single-cell expression, which is important for therapeutic decision making. For routine diagnostics, the combination of IHC and FISH is useful. In addition to improving the accuracy and comparability of HER2 assays, these optimized protocols may further enhance the efficacy of trastuzumab therapy by selecting those patients most likely to respond.

Radial and longitudinal diffusion of myoglobin in single living heart and skeletal muscle cells

We have used a fluorescence recovery after photobleaching (FRAP) technique to measure radial diffusion of myoglobin and other proteins in single skeletal and cardiac muscle cells. We compare the radial diffusivities, D(r) (i.e., diffusion perpendicular to the long fiber axis), with longitudinal ones, D(l) (i.e., parallel to the long fiber axis), both measured by the same technique, for myoglobin (17 kDa), lactalbumin (14 kDa), and ovalbumin (45 kDa). At 22 degrees C, D(l) for myoglobin is 1.2 x 10(-7) cm(2)/s in soleus fibers and 1.1 x 10(-7) cm(2)/s in cardiomyocytes. D(l) for lactalbumin is similar in both cell types. D(r) for myoglobin is 1.2 x 10(-7) cm(2)/s in soleus fibers and 1.1 x 10(-7) cm(2)/s in cardiomyocytes and, again, similar for lactalbumin. D(l) and D(r) for ovalbumin are 0.5 x 10(-7) cm(2)/s. In the case of myoglobin, both D(l) and D(r) at 37 degrees C are about 80% higher than at 22 degrees C. We conclude that intracellular diffusivity of myoglobin and other proteins (i) is very low in striated muscle cells, approximately 1/10 of the value in dilute protein solution, (ii) is not markedly different in longitudinal and radial direction, and (iii) is identical in heart and skeletal muscle. A Krogh cylinder model calculation holding for steady-state tissue oxygenation predicts that, based on these myoglobin diffusivities, myoglobin-facilitated oxygen diffusion contributes 4% to the overall intracellular oxygen transport of maximally exercising skeletal muscle and less than 2% to that of heart under conditions of high work load.

Effect of diet quantity and urea supplementation on oocyte and embryo quality in sheep

The objective was to investigate the effects of dietary energy and urea supplementation on oocyte and embryo quality in sheep using in vivo and in vitro experimental models. Sixty-three ewes were fed grass meal at 0.5 or 2.0 times maintenance energy requirements (MER). The diet was supplemented with feed grade urea (U) for half of the ewes on each energy treatment. Ewes were stimulated with 1000 IU eCG and either slaughtered on the day of pessary withdrawal, for in vitro embryo production, or mated and slaughtered on Day 5 for embryo recovery. Urea decreased cleavage rate (48.3 vs 39.7%) and consequently blastocyst rate (41.6 vs 36.8%) but the differences were not significant. Oocytes from animals on 2.0 MER had a lower cleavage rate (54.9 vs 36.0%) and blastocyst yield (49.3 vs 31.4%) than those on 0.5 MER. However, there was an interaction between urea and energy for cleavage (P = 0.04) and blastocyst yield (P = 0.03) indicating a variable response to urea in the presence of high energy. This was manifested by a decrease in cleavage rate in the presence of urea and high energy (22%, 8 of 36), and a reduction in blastocyst development (19%, 7 of 36). When blastocyst development rate was expressed as a proportion of cleaved oocytes there was no difference between groups; in addition, there was no difference between groups in terms of blastocyst hatching rate (overall mean 66.1%) or blastocyst cell number on Day 8 (overall mean +/- SEM, 138.4 +/- 9.0, n=61). The effect of urea on cleavage rate in vivo was more severe. Urea supplementation reduced (P<0.001) the cleavage rate (93 vs 62%). Despite this, the yield of blastocysts was unaffected. Oocytes from ewes on 0.5 MER exhibited a lower (P<0.05) cleavage rate than those on 2.0 MER (66 vs 87%). This effect was also apparent at the blastocyst stage (40.0 vs 50.9%), although the difference was no longer significant. There were no differences in hatching rate (overall mean 70.7%) or blastocyst cell numbers (overall mean +/- SEM, 166.3 +/- 15.6, n=40). Collectively, these results suggest that both high dietary energy and urea content influence subsequent embryo development in vitro, and the deleterious effects of urea are likely influenced by concomitant energy intake.

Extracellular carbonic anhydrase activity facilitates lactic acid transport in rat skeletal muscle fibres

1. In skeletal muscle an extracellular sarcolemmal carbonic anhydrase (CA) has been demonstrated. We speculate that this CA accelerates the interstitial CO2/HCO3- buffer system so that H+ ions can be rapidly delivered or buffered in the interstitial fluid. Because > 80 % of the lactate which crosses the sarcolemmal membrane is transported by the H+-lactate cotransporter, we examined the contributions of extracellular and intracellular CA to lactic acid transport, using ion-selective microelectrodes for measurements of intracellular pH (pHi) and fibre surface pH (pHs) in rat extensor digitorum longus (EDL) and soleus fibres. 2. Muscle fibres were exposed to 20 mM sodium lactate in the absence and presence of the CA inhibitors benzolamide (BZ), acetazolamide (AZ), chlorzolamide (CZ) and ethoxzolamide (EZ). The initial slopes (dpHs/dt, dpHi/dt) and the amplitudes (DeltapHs, DeltapHi) of pH changes were quantified. From dpHi/dt, DeltapHi and the total buffer factor (BFtot) the lactate fluxes (mM min-1) and intracellular lactate concentrations ([lactate]i) were estimated. 3. BFtot was obtained as the sum of the non-HCO3- buffer factor (BFnon-HCO3) and the HCO3- buffer factor (BFHCO3). BFnon-HCO3 was 35 +/- 4 mM pH-1 for the EDL (n = 14) and 86 /- 16 mM pH-1 for the soleus (n = 14). 4. In soleus, 10 mM cinnamate inhibited lactate influx by 44 % and efflux by 30 %; in EDL, it inhibited lactate influx by 37 % and efflux by 20 %. Cinnamate decreased [lactate]i, in soleus by 36 % and in EDL by 45 %. In soleus, 1 mM DIDS reduced lactate influx by 18 % and efflux by 16 %. In EDL, DIDS lowered the influx by 27 % but had almost no effect on efflux. DIDS reduced [lactate]i by 20 % in soleus and by 26 % in EDL. 5. BZ (0.01 mM) and AZ (0.1 mM), which inhibit only the extracellular sarcolemmal CA, led to a significant increase in dpHs/dt and pHs by about 40 %-150 % in soleus and EDL. BZ and AZ inhibited the influx and efflux of lactate by 25 %-50 % and reduced [lactate]i by about 40 %. The membrane-permeable CA inhibitors CZ (0.5 mM) and EZ (0.1 mM), which inhibit the extracellular as well as the intracellular CAs, exerted no greater effects than the poorly permeable inhibitors BZ and AZ did. 6. In soleus, 10 mM cinnamate inhibited the lactate influx by 47 %. Addition of 0.01 mM BZ led to a further inhibition by only 10 %. BZ alone reduced the influx by 37 %. 7. BZ (0.01 mM) had no influence on the Km value of the lactate transport, but led to a decrease in maximal transport rate (Vmax). In EDL, BZ reduced Vmax by 50 % and in soleus by about 25 %. 8. We conclude that the extracellular sarcolemmal CA plays an important role in lactic acid transport, while internal CA has no effect, a difference most likely attributable to the high internal vs. low extracellular BF(non-HCO3). The fact that the effects of cinnamate and BZ are not additive indicates that the two inhibitors act at distinct sites on the same transport pathway for lactic acid.

Anatomical variations in the internal jugular veins of cancer patients affecting central venous access. Anatomical variation of the internal jugular vein

PURPOSE

Establishing a reliable central venous access is an important procedure in clinical haematology and oncology. The purpose of this study was to determine how anatomical variations in the internal jugular vein (IJV) and its position in relation to the common carotid artery (CCA) in cancer patients affects external landmark puncture.

PATIENTS AND METHODS

In 113 patients with haematological or oncological diseases we examined sonographically potential target regions for placement of a central catheter via the IJV.

RESULTS

36% of our patients showed anatomical variations in the IJV and surrounding tissue.

CONCLUSIONS

External landmark puncture may be difficult in a considerable number of patients since the IJV might not be situated in the presumed location anteriorly or laterally to the CCA, or a normal lumen may not be present in approximately 1/3 of cancer patients. This study supports the use of ultrasound-guided techniques for central venous catheters particularly in haematological and oncological patients.

Protein diffusion in living skeletal muscle fibers: dependence on protein size, fiber type, and contraction

Sarcoplasmic protein diffusion was studied under different conditions, using microinjection in combination with microspectrophotometry. Six globular proteins with molecular masses between 12 and 3700 kDa, with diameters from 3 to 30 nm, were used for the experiments. Proteins were injected into single, intact skeletal muscle fibers taken from either soleus or extensor digitorum longus (edl) muscle of adult rats. No correlation was found between sarcomere spacing and the sarcoplasmic diffusion coefficient (D) for all proteins studied. D of the smaller proteins cytochrome c (diameter 3.1 nm), myoglobin (diameter 3.5 nm), and hemoglobin (diameter 5.5 nm) amounted to only approximately 1/10 of their value in water and was not increased by auxotonic fiber contractions. D for cytochrome c and myoglobin was significantly higher in fibers from edl (mainly type II fibers) compared to fibers from soleus (mainly type I fibers). Measurements of D for myoglobin at 37 degrees C in addition to 22 degrees C led to a Q(10) of 1.46 for this temperature range. For the larger proteins catalase (diameter 10.5 nm) and ferritin (diameter 12.2 nm), a decrease in D to approximately 1/20 and approximately 1/50 of that in water was observed, whereas no diffusive flux at all of earthworm hemoglobin (diameter 30 nm) along the fiber axis could be detected. We conclude that 1) sarcoplasmic protein diffusion is strongly impaired by the presence of the myofilamental lattice, which also gives rise to differences in diffusivity between different fiber types; 2) contractions do not cause significant convection in sarcoplasm and do not lead to increased diffusional transport; and 3) in addition to the steric hindrance that slows down the diffusion of smaller proteins, diffusion of large proteins is further hindered when their dimensions approach the interfilament distances. This molecular sieve property progressively reduces intracellular diffusion of proteins when the molecular diameter increases to more than approximately 10 nm.