Biomedical subjects

P D Brown

Publications and source records attributed to P D Brown.

At least 19 recordsLinked to original sources

PubMed2006

KCC3 and KCC4 expression in rat adult forebrain.

Potassium chloride ion cotransporters (KCCs) are part of a family of transporters classically described as being involved in cell volume regulation. Recently, KCC2 has been shown to have a role in the development of the inhibitory actions of amine transmitters, whereas KCC3 also plays a fundamental role in the development and function of the central and peripheral nervous system. We have re-assessed the expression of each of the known KCCs in the rat forebrain using RT-PCR and in situ hybridisation histochemistry. As well as confirming the widespread expression of KCC1 and KCC2 throughout the brain, we now show a more restricted expression of KCC3a in the hippocampus, choroid plexus and piriform cortex, as well as KCC4 in the choroid plexus and the suprachiasmatic nucleus of the hypothalamus. The expression of KCC4 in the latter and KCC2 in the lateral hypothalamic and ventromedial hypothalamic nuclei suggests that these cotransporters may have selective roles in neuroendocrine or homeostatic functions. Finally, we demonstrate the existence of a truncated splice variation of KCC3a in the rat that appears to be expressed exclusively in neurons (as is KCC2), whereas the native form of KCC3a and KCC4 appears to be expressed in glial cells.

Animals↗

PubMed2006

Molecular detection of QTLs for agronomic and quality traits in a doubled haploid population derived from two Canadian wheats (Triticum aestivum L.).

Development of high-yielding wheat varieties with good end-use quality has always been a major concern for wheat breeders. To genetically dissect quantitative trait loci (QTLs) for yield-related traits such as grain yield, plant height, maturity, lodging, test weight and thousand-grain weight, and for quality traits such as grain and flour protein content, gluten strength as evaluated by mixograph and SDS sedimentation volume, an F1-derived doubled haploid (DH) population of 185 individuals was developed from a cross between a Canadian wheat variety "AC Karma" and a breeding line 87E03-S2B1. A genetic map was constructed based on 167 marker loci, consisting of 160 microsatellite loci, three HMW glutenin subunit loci: Glu-A1, Glu-B1 and Glu-D1, and four STS-PCR markers. Data for investigated traits were collected from three to four environments in Manitoba, Canada. QTL analyses were performed using composite interval mapping. A total of 50 QTLs were detected, 24 for agronomic traits and 26 for quality-related traits. Many QTLs for correlated traits were mapped in the same genomic regions forming QTL clusters. The largest QTL clusters, consisting of up to nine QTLs, were found on chromosomes 1D and 4D. HMW glutenin subunits at Glu-1 loci had the largest effect on breadmaking quality; however, other genomic regions also contributed genetically to breadmaking quality. QTLs detected in the present study are compared with other QTL analyses in wheat.

Analysis of Variance↗

PubMed2005

Thin-film theories for two-phase reactive flow models of active cell motion.

The aim of this paper is to develop a broadly-applicable and self-consistent thin-film biphasic modelling framework for the full crawling cycle of a single animal cell. A hierarchy of thin-film two-phase 'reactive flow' models is derived; between them these cover a wide range of biologically relevant parameter regimes. The mathematical properties and biological implications of the resulting systems of high-order nonlinear degenerate parabolic-elliptic evolution equations are investigated. Linear-stability arguments suggest the formation of highly localized regions of high or low network density associated with small irregular oscillations or 'ruffling' of the plasma membrane. Local analyses at the contact line identify the classes of admissible contact-line conditions, through which we study for the first time the effect on the cell-scale motion of the 'mesoscopic' contact-line physics, which consists of the chemical and mechanical mechanisms for protrusive and retractive force generation near the outer cell periphery. One of the formulations is used to develop a minimal model for cell body translocation over a thin pseudopod, which predicts that myosin-driven contraction is not essential for rapid translocation. An analytic prediction for the translocation speed is given in terms of the network viscosity and slip coefficient (a parameter measuring the adhesion strength), of the membrane tension and of the thicknesses of the pseudopod and actin cortex; this is in good agreement with the translocation speed of osteoblasts on biomaterial substrates commonly used for orthopaedic implants. Limitations of the modelling approach and directions for future work are outlined.

Actins↗

PubMed2004

Tolbutamide potentiates the volume-regulated anion channel current in rat pancreatic beta cells.

AIMS/HYPOTHESIS: Hypoglycaemic sulphonylureas are thought to stimulate insulin release by binding to a sulphonylurea receptor, closing K(ATP) channels and inducing electrical activity. However, the fact that these drugs stimulate insulin release at high glucose concentrations where K(ATP) channels are closed suggests additional ionic actions. The aim of this study was to test the hypothesis that sulphonylureas influence the current of the glucose- and volume-regulated anion channel. METHODS: Electrical and ion-channel activity were recorded in isolated rat beta cells using the patch-clamp technique. (86)Rb(+) efflux was measured using intact islets. Beta cell volume was measured using a video-imaging technique. RESULTS: In the absence of glucose, tolbutamide (100 micromol/l) transiently depolarised the cells. In the presence of glucose (5 mmol/l), tolbutamide evoked a sustained period of electrical activity, whilst at 10 mmol/l glucose, the drug evoked a pronounced 'silent' depolarisation. In the absence of glucose, tolbutamide inhibited (86)Rb(+) efflux. However, at 10 mmol/l glucose, tolbutamide induced a transient stimulation of efflux. Tolbutamide potentiated the whole-cell volume-regulated anion conductance in a glucose-dependent manner with an EC(50) of 85 micromol/l. In single channel recordings, tolbutamide increased the channel-open probability. Tolbutamide caused beta cell swelling in the presence of glucose, but not in its absence. CONCLUSIONS/INTERPRETATION: Tolbutamide can induce beta cell electrical activity by potentiating the glucose- and volume-regulated anion channel current. This effect is probably not due to a direct effect of the drug on the channel, but could be secondary to a metabolic action in the beta cell.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗

PubMed2004

Molecular mechanisms of cerebrospinal fluid production.

The epithelial cells of the choroid plexuses secrete cerebrospinal fluid (CSF), by a process which involves the transport of Na(+), Cl(-) and HCO(3)(-) from the blood to the ventricles of the brain. The unidirectional transport of ions is achieved due to the polarity of the epithelium, i.e. the ion transport proteins in the blood-facing (basolateral) membrane are different to those in the ventricular (apical) membrane. The movement of ions creates an osmotic gradient which drives the secretion of H(2)O. A variety of methods (e.g. isotope flux studies, electrophysiological, RT-PCR, in situ hybridization and immunocytochemistry) have been used to determine the expression of ion transporters and channels in the choroid plexus epithelium. Most of these transporters have now been localized to specific membranes. For example, Na(+)-K(+)ATPase, K(+) channels and Na(+)-2Cl(-)-K(+) cotransporters are expressed in the apical membrane. By contrast the basolateral membrane contains Cl(-)- HCO(3) exchangers, a variety of Na(+) coupled HCO(3)(-) transporters and K(+)-Cl(-) cotransporters. Aquaporin 1 mediates water transport at the apical membrane, but the route across the basolateral membrane is unknown. A model of CSF secretion by the mammalian choroid plexus is proposed which accommodates these proteins. The model also explains the mechanisms by which K(+) is transported from the CSF to the blood.

Animals↗

PubMed2002

A double-blind placebo-controlled, randomised study comparing gemcitabine and marimastat with gemcitabine and placebo as first line therapy in patients with advanced pancreatic cancer.

Pancreatic cancer is the fifth most common cause of cancer death in the western world and the prognosis for unresectable disease remains poor. Recent advances in conventional chemotherapy and the development of novel 'molecular' treatment strategies with different toxicity profiles warrant investigation as combination treatment strategies. This randomised study in pancreatic cancer compares marimastat (orally administered matrix metalloproteinase inhibitor) in combination with gemcitabine to gemcitabine alone. Two hundred and thirty-nine patients with unresectable pancreatic cancer were randomised to receive gemcitabine (1000 mg m(-2)) in combination with either marimastat or placebo. The primary end-point was survival. Objective tumour response and duration of response, time to treatment failure and disease progression, quality of life and safety were also assessed. There was no significant difference in survival between gemcitabine and marimastat and gemcitabine and placebo (P=0.95 log-rank test). Median survival times were 165.5 and 164 days and 1-year survival was 18% and 17% respectively. There were no significant differences in overall response rates (11 and 16% respectively), progression-free survival (P=0.68 log-rank test) or time to treatment failure (P=0.70 log-rank test) between the treatment arms. The gemcitabine and marimastat combination was well tolerated with only 2.5% of patients withdrawn due to presumed marimastat toxicity. Grade 3 or 4 musculoskeletal toxicities were reported in only 4% of the marimastat treated patients, although 59% of marimastat treated patients reported some musculoskeletal events. The results of this study provide no evidence to support a combination of marimastat with gemcitabine in patients with advanced pancreatic cancer. The combination of marimastat with gemcitabine was well tolerated. Further studies of marimastat as a maintenance treatment following a response or stable disease on gemcitabine may be justified.

Adenocarcinoma↗

PubMed2002

Marimastat as maintenance therapy for patients with advanced gastric cancer: a randomised trial.

This randomised, double-blind, placebo-controlled study was designed to evaluate the ability of the orally administered matrix metalloproteinase inhibitor, marimastat, to prolong survival in patients with non-resectable gastric and gastro-oesophageal adenocarcinoma. Three hundred and sixty-nine patients with histological proof of adenocarcinoma, who had received no more than a single regimen of 5-fluorouracil-based chemotherapy, were randomised to receive either marimastat (10 mg b.d.) or placebo. Patients were treated for as long as was tolerable. The primary endpoint was overall survival with secondary endpoints of time to disease progression and quality of life. At the point of protocol-defined study completion (85% mortality in the placebo arm) there was a modest difference in survival in the intention-to-treat population in favour of marimastat (P=0.07 log-rank test, hazard ratio=1.23 (95% confidence interval 0.98-1.55)). This survival benefit was maintained over a further 2 years of follow-up (P=0.024, hazard ratio=1.27 (1.03-1.57)). The median survival was 138 days for placebo and 160 days for marimastat, with 2-year survival of 3% and 9% respectively. A significant survival benefit was identified at study completion in the pre-defined sub-group of 123 patients who had received prior chemotherapy (P=0.045, hazard ratio=1.53 (1.00-2.34)). This benefit increased with 2 years additional follow-up (P=0.006, hazard ratio=1.68 (1.16-2.44)), with 2-year survival of 5% and 18% respectively. Progression-free survival was also significantly longer for patients receiving marimastat compared to placebo (P=0.009, hazard ratio=1.32 (1.07-1.63)). Marimastat treatment was associated with the development of musculoskeletal pain and inflammation. Events of anaemia, abdominal pain, jaundice and weight loss were more common in the placebo arm. This is one of the first demonstrations of a therapeutic benefit for a matrix metalloproteinase inhibitor in cancer patients. The greatest benefit was observed in patients who had previously received chemotherapy. A further randomised study of marimastat in these patients is warranted.

Adenocarcinoma↗

PubMed2001

Marimastat as first-line therapy for patients with unresectable pancreatic cancer: a randomized trial.

PURPOSE: The prognosis for unresectable pancreatic cancer remains dismal (1-year survival rate, < 10%; 5-year survival rate, < 5%). Recent advances in conventional chemotherapy and novel molecular treatment strategies warrant investigation. This, the largest randomized study in pancreatic cancer performed to date, compares marimastat, the first of a new class of agents, with gemcitabine. PATIENTS AND METHODS: Four hundred fourteen patients with unresectable pancreatic cancer were randomized to receive marimastat 5, 10, or 25 mg bid or gemcitabine 1,000 mg/m2. The primary end point was survival. Progression-free survival, patient benefit, and safety were also assessed. RESULTS: There was no significant difference in survival between 5, 10, or 25 mg of marimastat and gemcitabine (P =.19). Median survival times were 111, 105, 125, and 167 days, respectively, and 1-year survival rates were 14%, 14%, 20%, and 19%, respectively. There was a significant difference in survival rates between patients treated with gemcitabine and marimastat 5 and 10 mg (P <.003). Both agents were well tolerated, although grade 3 or 4 toxicities were reported in 22% and 12% of the gemcitabine- and marimastat-treated patients, respectively. The major toxicity of marimastat was musculoskeletal (44% of marimastat patients, compared with 12% of gemcitabine patients; musculoskeletal toxicity was severe in only 8% of marimastat patients). CONCLUSION: The results of this study provide evidence of a dose response for marimastat in patients with advanced pancreatic cancer. The 1-year survival rate for patients receiving marimastat 25 mg was similar to that of patients receiving gemcitabine. In view of the manageable tolerability of marimastat and its ease of administration, further studies are warranted.

Adenocarcinoma↗

PubMed2001

Expression of volume-sensitive Cl(-) channels and ClC-3 in acinar cells isolated from the rat lacrimal gland and submandibular salivary gland.

1. The expression of ClC-3 was examined in rat lacrimal gland and submandibular salivary gland cells using RT-PCR and Western analysis. Whole-cell patch clamp methods were used to investigate the expression of volume-sensitive anion channels in acinar cells isolated from these tissues. 2. Expression of mRNA encoding ClC-3, and ClC-3 protein, was found in rat submandibular gland by RT-PCR and Western analysis. Rat lacrimal gland cells, however, did not appear to express mRNA encoding for ClC-3, nor the ClC-3 protein. 3. Volume-sensitive anion conductances were observed in both rat lacrimal gland and submandibular salivary gland acinar cells. The conductance was of a similar size in the two cell types, but was much slower to activate in the lacrimal cells. 4. The properties of the conductances in lacrimal and submandibular cells were similar, e.g. halide selectivity sequence (P(I) > P(Cl) > P(aspartate)) and inhibition by 4,4'-diisothiocyanostilbene-2,2'-disulphonic acid, 5-nitro-2-(3-phenylpropylamino)-benzoate and tamoxifen. 5. The data suggest that the expression of ClC-3 is not an absolute requirement for the activity of volume-sensitive anion channels in rat lacrimal gland acinar cells.

Animals↗

PubMed2001

Swelling-induced changes in cytosolic [Ca2++] in insulin-secreting cells: a role in regulatory volume decrease?

Exposure of insulin-secreting cells to hypotonic solutions causes cell swelling followed by regulatory volume decrease (RVD). We have previously demonstrated that RVD is due to activation of a Cl(-) conductance. The present study investigates whether changes in cytosolic [Ca(2+)] play a role in these responses. Hypotonic swelling of RINm5F insulinoma cells caused a marked increase in cytosolic [Ca(2+)]. This effect was abolished by omission of extracellular Ca(2+), by the Ca(2+) channel blockers D600 or Gd(3+)and by 4,4'-dithiocyanatostilbene-2,2'-disulphonic acid (DIDS), an inhibitor of the volume-sensitive anion. RVD was markedly impaired in the absence of extracellular Ca(2+), but not by D600 nor by Gd(3+). RVD was also inhibited by the maxi-K(+) (BK(Ca)) channel blockers tetraethylammonium (TEA) and iberiotoxin (IbTx), whereas the K(ATP) channel blocker tolbutamide was ineffective. Cell swelling was accompanied by activation of a K(+) conductance which was sensitive to TEA and IbTx but not to tolbutamide. It is concluded that cell swelling causes activation of the volume-sensitive anion channel, leading to depolarization and Ca(2+) entry via voltage-gated Ca(2+) channels. RVD is a Ca(2+)-dependent process, requiring low 'resting' levels of intracellular [Ca(2+)]. However, the swelling-induced increase in cytosolic [Ca(2+)] is not required for RVD to occur. RVD depends upon simultaneous activation of Cl(-) and K(+) channels. We suggest that the BK(Ca) channel is the major K(+) conductance involved in RVD.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗

PubMed2001

Mechanisms of CSF secretion by the choroid plexus.

The epithelial cells of the choroid plexus secrete cerebrospinal fluid (CSF), by a process that involves the movement of Na(+), Cl(-) and HCO(3)(-) from the blood to the ventricles of the brain. This creates the osmotic gradient, which drives the secretion of H(2)O. The unidirectional movement of the ions is achieved due to the polarity of the epithelium, i.e., the ion transport proteins in the blood-facing (basolateral) are different to those in the ventricular (apical) membranes. Saito and Wright (1983) proposed a model for secretion by the amphibian choroid plexus, in which secretion was dependent on activity of HCO(3)(-) channels in the apical membrane. The patch clamp method has now been used to study the ion channels expressed in rat choroid plexus. Two potassium channels have been observed that have a role in maintaining the membrane potential of the epithelial cell, and in regulating the transport of K(+) across the epithelium. An inward-rectifying anion channel has also been identified, which is closely related to ClC-2 channels, and has a significant HCO(3)(-) permeability. This channel is expressed in the apical membrane of the epithelium where it may play an important role in CSF secretion. A model of CSF secretion by the mammalian choroid plexus is proposed that accommodates these channels and other data on the expression of transport proteins in the choroid plexus.

Animals↗

PubMed2001

Pyrethroid insecticide residues on vegetable crops.

Pyrethroid insecticides were applied on various vegetable crops as foliar treatments to determine dissipation rates. On Chinese broccoli (Guy Lon), Chinese mustard (Pak Choi) and Chinese cabbage (Kasumi, napa), fenvalerate was persistent with residues of 0.10, 0.14 and 0.11 mg kg-1, respectively, by day 21. Cypermethrin residues on head lettuce were below 0.1 mg kg-1 by day 10 but on the leafier romaine and endive varieties it was more persistent and required 14-19 days to dissipate below this concentration. After three applications, residues of cypermethrin in harvested carrots and of permethrin in eggplant were not detected on the day of application. On asparagus, deltamethrin and cypermethrin residues declined to less than 0.1 mg kg-1 by days 1 and 2, respectively; permethrin was more persistent, requiring more than 2 days to decline to less than 0.1 mg kg-1. Deltamethrin on dry (cooking) and Spanish onions was not detected on the day of application. On tomatoes, the concentration of permethrin was 0.093 mg kg-1 on the day of application and declined to about 0.05 mg kg-1 after 2-4 days. In general, permethrin, cypermethrin and deltamethrin residues declined to acceptable concentrations within an acceptable pre-harvest interval. Fenvalerate may be too persistent on these speciality crops unless a maximum residue limit > 0.1 mg kg-1 is permitted.

Crops, Agricultural↗

PubMed2001

Expression of the Na+K+-2CI- cotransporter in alpha and beta cells isolated from the rat pancreas.

The expression of the Na+-K+-2Cl- cotransporter (NKCC1) in alpha cells and beta cells from the rat pancreas was examined. Isolated alpha cells and beta cells in a mixed islet cell preparation were identified by volume using video-imaging methods, and by the expression of glucagon or insulin. The expression of mRNA for NKCC1 in pancreatic islets was demonstrated by RT-PCR. Immunocytochemical studies showed that the NKCCI protein was expressed in rat beta cells, but not alpha cells. The activity of Na+-K+-2Cl- cotransporter was also examined, by studying cell volume regulation in response to HEPES-buffered, hypertonic solutions. A regulatory volume increase was observed in the beta cells but not the alpha cells. It is concluded that the NKCC1 is expressed in rat pancreatic beta cells but not alpha cells. This is consistent with the hypothesis that Cl- is accumulated above the expected equilibrium distribution in beta cells, but is below equilibrium in alpha cells.

Animals↗

PubMed2001

Identification and regulation of K+ and Cl- channels in human parotid acinar cells.

The properties of K+ channels in these cells were studied using patch-clamp methods. Two channels, with conductances of 165+/-13 pS (n=6) and 30+/-1 pS (n=3), were identified in single-channel experiments. In cell-attached patches the reversal potentials were -67+/-8 and -74+/-2 mV for the large and small conductance channel, respectively, suggesting that both channels are K+-selective. The large conductance channel was also shown to be K+-selective in inside-out patches. The open probability (P(o)) of this channel was increased at depolarizing potentials and by increasing intracellular Ca2+ concentration ([Ca2+]i). These properties suggest that the large conductance channel is a 'maxi' Ca2+-activated K+ channel (BK(Ca)). The small conductance channel was not observed in inside-out patches. Carbachol (CCh; 10(-5) M) activated the BK(Ca) channel, but not the small conductance channel, in cell-attached patches. CCh also caused a dose-dependent increase in [Ca2+]i measured by fura-2 in microspectrofluorimetric studies, with a half-maximal response at approximately 3x10(-6) M. Neither isoproterenol (10(-5) M) nor substance P (10(-6) M) affected K+-channel activity or [Ca2+]i. In whole-cell experiments, CCh caused an increase in outward current. Charybdotoxin (10(-7) M), a BK(Ca) blocker, inhibited a large component of the CCh-induced current. A large component of the charybdotoxin-insensitive current may be carried by Ca2+-activated Cl- channels, which were also observed in human parotid acinar cells. The results indicate that BK(Ca) channels make a significant contribution to the whole-cell conductance in human parotid acinar cells.

Adult↗

PubMed2001

The biosynthesis of benzoic acid glucosinolate esters in Arabidopsis thaliana.

The siliques and seeds of Arabidopsis thaliana accumulate a series of glucosinolates containing an alkyl side chain of varying length with a terminal benzoate ester function. The biosynthesis of these unusual nitrogen- and sulfur-containing natural products was investigated by feeding isotopically-labeled precursors to detached flowering stems. Glucosinolates were extracted, purified and analyzed by tandem mass spectrometry. Phenylalanine and benzoic acid were incorporated into the benzoate ester function, and methionine and acetate were incorporated into the aliphatic portion of the side chain in a position-specific manner. The labeling patterns observed were consistent with the chain extension of methionine by a three-step elongation cycle which begins with the condensation of acetyl-CoA with a 2-oxo acid derived from methionine and ends with an oxidative decarboxylation forming a new 2-oxo acid with an additional methylene group. Incorporation of desulfo-4-methylthiobutyl glucosinolate into 4-benzoyloxybutyl olucosinolate suggested chain-extended methionine derivatives are first converted to their corresponding methylthioalkyl glucosinolates with further side chain modification occurring later. Transformation of the methylthiol function to a hydroxyl group is followed by esterification with benzoic acid. The siliques appear to possess the complete machinery for carrying out all of the reactions in the biosyntheis of these complex glucosinolates.

Amino Acids↗

PubMed2001

Long-term results of a phase I/II study of high-dose thoracic radiotherapy with concomitant cisplatin and etoposide in limited stage small-cell lung cancer.

This report presents the results from a Mayo Clinic initiated phase I/II study exploring a potentially more aggressive local and systemic approach for treatment of limited-stage small-cell lung cancer (LSSCLC). Five patients with LSSCLC received three cycles of induction cyclophosphamide, etoposide, and infusion cisplatin chemotherapy. This was followed by accelerated hyperfractionated thoracic radiotherapy (AHFTRT) consisting of 30 Gy given as 1.5-Gy fractions twice daily with a 2-week break and then the AHFTRT was repeated. The AHFTRT was given concomitantly with daily oral etoposide and daily intravenous cisplatin. Prophylactic cranial radiation was delivered with the AHFTRT. After completion of the AHFTRT, patients received 4 cycles of oral etoposide maintenance chemotherapy. Follow-up of patients was continued until death or a minimum of 42 months. Three patients had severe toxic responses. No patients completed the entire protocol because of toxicity or progression during treatment. Three patients completed the majority of the protocol except for the four cycles of maintenance etoposide. Four of five patients achieved a complete response. There were two recurrences within the irradiated field, and distant metastases developed in four patients. Acute nonlymphocytic leukemia developed in one patient, who died 2 months later. No patient completed the entire protocol, because of toxicity or progression; therefore, this protocol cannot be recommended for the treatment of LSSCLC.

Adult↗

PubMed2000

An analysis of facial nerve function in irradiated and unirradiated facial nerve grafts.

PURPOSE: The effect of high-dose radiation therapy on facial nerve grafts is controversial. Some authors believe radiotherapy is so detrimental to the outcome of facial nerve graft function that dynamic or static slings should be performed instead of facial nerve grafts in all patients who are to receive postoperative radiation therapy. Unfortunately, the facial function achieved with dynamic and static slings is almost always inferior to that after facial nerve grafts. In this retrospective study, we compared facial nerve function in irradiated and unirradiated nerve grafts. METHODS AND MATERIALS The medical records of 818 patients with neoplasms involving the parotid gland who received treatment between 1974 and 1997 were reviewed, of whom 66 underwent facial nerve grafting. Fourteen patients who died or had a recurrence less than a year after their facial nerve graft were excluded. The median follow-up for the remaining 52 patients was 10.6 years. Cable nerve grafts were performed in 50 patients and direct anastomoses of the facial nerve in two. Facial nerve function was scored by means of the House-Brackmann (H-B) facial grading system. Twenty-eight of the 52 patients received postoperative radiotherapy. The median time from nerve grafting to start of radiotherapy was 5.1 weeks. The median and mean doses of radiation were 6000 and 6033 cGy, respectively, for the irradiated grafts. One patient received preoperative radiotherapy to a total dose of 5000 cGy in 25 fractions and underwent surgery 1 month after the completion of radiotherapy. This patient was placed, by convention, in the irradiated facial nerve graft cohort. RESULTS: Potential prognostic factors for facial nerve function such as age, gender, extent of surgery at the time of nerve grafting, preoperative facial nerve palsy, duration of preoperative palsy if present, or number of previous operations in the parotid bed were relatively well balanced between irradiated and unirradiated patients. However, the irradiated graft group had a greater proportion of patients with pathologic evidence of nerve invasion (p = 0.007) and unfavorable type of nerve graft (p = 0.04). Although the irradiated graft cohort had more potentially negative prognostic factors, there was no difference in functional outcome (H-B Grade III or IV) between irradiated and unirradiated graft patients. H-B Grades III, IV, V, and VI were the best postoperative facial nerve functions achieved in 35%, 39%, 13%, and 13% of patients, respectively. The patient with preoperative radiotherapy never recovered any facial nerve function (H-B Grade VI). Median time to best facial nerve function after surgery was longer in the irradiated patients (13.1 vs. 10.8 months), but this was not statistically significant (p = 0.10). Presence of preoperative facial nerve palsy (p = 0.005), duration of preoperative palsy (p = 0.003), and age greater than 60 years at the time of grafting (p = 0. 04) were all negative prognostic factors for achieving a functional facial nerve on univariate analysis. Analysis of age as a continuous variable (p = 0.12) and pathologic evidence of nerve invasion (p = 0. 1) revealed a trend toward negative prognostic factors. Gender, number of previous operations in the parotid bed, extent of surgery at the time of nerve grafting, and type of grafting procedure were not significant prognostic factors. Whether radiotherapy was delivered less than 6 weeks after nerve grafting or more than 6 weeks had no impact on achievement of a functional facial nerve. CONCLUSION: Negative prognostic factors for achieving a functional facial nerve in our series include the presence of preoperative facial nerve palsy, duration of preoperative palsy, and age greater than 60 years. Radiotherapy was not a negative prognostic factor. Comparing irradiated and unirradiated grafts revealed no difference in best facial nerve function achieved, despite the presence of a greater proportion of negative prognostic factors in

Adolescent↗

PubMed2000

Selective inhibition of glucose-stimulated beta-cell activity by an anion channel inhibitor.

4,4'-Dithiocyanatostilbene-2,2'-disulfonic acid (DIDS), an inhibitor of the volume-sensitive anion channel, was used to investigate the role of this channel in the stimulation of rat pancreatic beta-cells by glucose and by tolbutamide. Glucose-stimulated electrical activity in beta-cells was markedly and reversibly inhibited by DIDS. The increase in cytosolic [Ca2+] and stimulated insulin release evoked by glucose were also inhibited by DIDS. In contrast to its inhibitory effect on glucose-induced beta-cell activity, DIDS had no effect on electrical activity, the rise in [Ca2+]i or insulin release induced by tolbutamide. DIDS failed to increase beta-cell input conductance, an index of whole-cell K(ATP) channel activity, or the rate of efflux of 86Rb+ from perifused islets, a measure of net K+ permeability. Furthermore, DIDS had no effect on intracellular pH or on regulatory volume increase following exposure of cells to hypertonic solutions, indicating that the effects of DIDS were not the result of inhibition of Cl- transport systems. It is suggested that the DIDS-induced repolarization is caused by inactivation of the volume-sensitive anion channel. The stimulation of beta-cell electrical and secretory activity by glucose, but not tolbutamide, may therefore involve activation of the anion channel.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗