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T M Egan

Publications and source records attributed to T M Egan.

At least 37 records · Page 2Linked to original sources
PubMed1998

Neuropeptide Y receptors involved in calcium channel regulation in PC12 cells.

Our laboratory has previously used NGF-differentiated PC12 cells as a sympathetic neuronal model to investigate the effects of NPY on catecholamine synthesis and release. We have additionally used these cells to demonstrate the NPY-induced inhibition of Ca2+ channels which was suggested by those studies. In the present work, multiple NPY, PYY, and PP analogs are utilized to further define the receptor subtypes involved in this Ca2+ channel modulation. We find that in PC12 cells NPY and PP modulate Ca2+ channels through Y1, Y2, Y3, and Y4 receptors. In addition, we show that these receptors are differentially coupled to N, L, and non-N, non-L Ca2+ channel subtypes. The results of the present study in combination with our previous investigations demonstrate an intriguing and complex role for NPY and PP in the modulation of sympathetic neurotransmission.

Animals↗
PubMed1998

A domain contributing to the ion channel of ATP-gated P2X2 receptors identified by the substituted cysteine accessibility method.

P2X receptors are a family of ATP-gated ion channels thought to have intracellular N and C termini and two transmembrane segments separating a large extracellular domain. We examined the involvement of the second putative transmembrane domain (TM2) of the P2X2 subunit in ion conduction, using the substituted cysteine accessibility method (SCAM). This method tests the ability of hydrophilic reagents such as Ag+ or the methanethiosulfonates to modify covalently the sulfhydryl side chains exposed to aqueous environments. ATP-gated current was measured in HEK293 cells transiently expressing either wild-type or functional mutant P2X2 receptors containing a cysteine substitution in or around TM2. Application of Ag+ to gating channels had no sustained effect on wild-type P2X2 (WT) but irreversibly altered whole-cell currents in 15 mutants. By contrast, bath application of (2-aminoethyl)methanethiosulfonate (MTSEA) to closed channels inhibited 8 of the 15 residues affected by Ag+ when the channel was gating. Inhibition of the closed channel was prevented in seven of eight mutants when membrane-permeant MTSEA was scavenged by 20 mM intracellular cysteine, indicating that these seven mutants lie on the intracellular side of the channel gate. Further, MTSEA inhibited current through G342C in the absence of intracellular cysteine but augmented the current when cysteine was present, suggesting that this residue may be part of the gate. Taken together, the data help to the identify a functional domain of the channel pore by mapping residues on either side of the channel gate.

Adenosine Triphosphate↗
PubMed1998

Topological analysis of the ATP-gated ionotropic [correction of ionotrophic] P2X2 receptor subunit.

We investigated the transmembrane topology of the P2X2 receptor subunit expressed in HEK 293 cells. Initial studies using two P2X subunits expressed in tandem indicated that the amino- and carboxy-termini are on the same side of the membrane. Immunofluorescence studies showed the cytoplasmic orientation of the amino- and carboxy-termini. Finally, N-glycosylation scanning mutagenesis revealed that reporter sites inserted into the central loop, but not those in the amino- or carboxy-terminal regions, were glycosylated, thus suggesting an extracellular placement for that domain. Our results support a two-transmembrane arrangement for P2X receptors with intracellular amino- and carboxy-termini.

Adenosine Triphosphate↗
PubMed1998

Lung transplantation for cystic fibrosis: effective and durable therapy in a high-risk group.

BACKGROUND: The purpose of this study was to review our experience with lung transplantation in patients with end-stage cystic fibrosis. METHODS: Eight-two patients with cystic fibrosis have undergone bilateral lung transplantation (n=76) or bilateral lower lobe transplantation (n=6) since October 1990. RESULTS: Actuarial survival for the entire cohort is 79% at 1 year and 57% at 5 years. The development of bronchiolitis obliterans syndrome is the leading cause of death after the first year. Freedom from bronchiolitis obliterans syndrome is 84% at 1 year and 51% at 3 years. Pulmonary function tests improve dramatically in recipients. There was no association between death within 1 year and recipient age, weight, graft ischemic time, cytomegalovirus seronegativity, or the presence of pan-resistant organisms. Similarly, there was no association between the development of bronchiolitis obliterans syndrome within 2 years and ischemic time, number of rejection episodes, cytomegalovirus seronegativity, or the presence of panresistant organisms. CONCLUSIONS: Despite their poor nutritional status and the presence of multiply resistant organisms, patients with cystic fibrosis can undergo bilateral lung transplantation with acceptable morbidity and mortality.

Adolescent↗
PubMed1998

Co-expression of P2X1 and P2X5 receptor subunits reveals a novel ATP-gated ion channel.

P2X receptors are a family of ion channels gated by extracellular ATP. Each member of the family can form functional homomeric channels, but only P2X2 and P2X3 have been shown to combine to form a unique heteromeric channel. Data from in situ hybridization studies suggest that P2X1 and P2X5 may also co-assemble. In this study, we tested this hypothesis by expressing recombinant P2X1 and P2X5 receptor subunits either individually or together in human embryonic kidney 293 cells. In cells expressing the homomeric P2X1 receptor, 30 microM alpha,beta-methylene ATP (alpha,beta-me-ATP) evoked robust currents that completely desensitized in less than 1 sec, whereas alpha,beta-me-ATP failed to evoke current in cells expressing the homomeric P2X5 receptor. By contrast, alpha, beta-me-ATP evoked biphasic currents with a pronounced nondesensitizing plateau phase in cells that co-expressed both subunits. Further, the EC50 for alpha,beta-me-ATP was greater in cells expressing both P2X1 and P2X5 than in cells expressing P2X1 alone (5 and 1.6 microM, respectively). Heteromeric assembly was confirmed using a co-immunoprecipitation assay of epitope-tagged P2X1 and P2X5 subunits. In summary, this study provides biochemical and functional evidence of a novel channel formed by P2X subunit heteropolymerization. This finding suggests that heteromeric subunit assembly constitutes an important mechanism for generating functional diversity of ATP-mediated responses.

Adenosine Triphosphate↗
PubMed1998

Neuropeptide Y inhibition of calcium channels in PC-12 pheochromocytoma cells.

We previously demonstrated, using rat PC-12 pheochromocytoma cells differentiated to a sympathetic neuronal phenotype with nerve growth factor (NGF), that neuropeptide Y (NPY) inhibits catecholamine synthesis as well as release. Inquiry into the mechanisms of these inhibitions implicated distinct pathways involving reduction of Ca2+ influx through voltage-activated Ca2+ channels. In the present investigation the effects of NPY on whole cell Ba2+ currents were examined to obtain direct evidence supporting the mechanisms suggested by those studies. NPY was found to inhibit the voltage-activated Ba2+ current in NGF-differentiated PC-12 cells in a reversible fashion with an EC50 of 13 nM. This inhibition was pertussis toxin sensitive and resulted from NPY modulation of L- and N-type Ca2+ channels. The inhibition of L-type channels was not seen with < 1 nM free intracellular Ca2+ or when protein kinase C (PKC) was inhibited by chelerythrine or PKC-(19-31). Furthermore, the effect of NPY on L-type channels was mimicked by the PKC activator phorbol 12-myristate 13-acetate. These studies demonstrate that, in addition to inhibition of N-type Ca2+ channels, in NGF-differentiated PC-12 cells NPY inhibits L-type Ca2+ channels via an intracellular Ca(2+)- and PKC-dependent pathway.

Alkaloids↗
PubMed1997

Reduced ischemia-reperfusion injury with isoproterenol in non-heart-beating donor lungs.

Transplantation of lungs retrieved from non-heart-beating donors could expand the donor pool. Recent studies suggest that the ischemia-reperfusion injury (IRI) to the lung can be attenuated by increasing intracellular cAMP concentrations. The purpose of this study was to determine the effect of IRI on capillary permeability, as measured by Kfc, in lungs retrieved from non-heart-beating donors and reperfused with or without isoproterenol (iso). Using an in situ isolated perfused lung model, lungs were retrieved from non-heart-beating donor rats ventilated with O2 or not at varying intervals after death. The lungs were reperfused with or without iso (10 microM). Kfc, lung viability, and pulmonary hemodynamics were measured, and tissue levels of adenine nucleotides and cAMP were measured by HPLC. Iso-reperfusion decreased Kfc significantly (P < 0.05) compared to non-iso-reperfused groups at all postmortem ischemic times, irrespective of preharvest ventilation status. Pulmonary arterial pressures and resistances increased and venous resistances decreased with iso-reperfusion. Total adenine nucleotide (TAN) levels correlated with Kfc in non-iso-reperfused (r = 0.65) and iso-perfused (r = 0.84) lungs. cAMP levels increased significantly with iso-reperfusion. cAMP levels correlated with Kfc (r = 0.87) in iso-reperfused lungs. Iso-reperfusion of lungs retrieved from non-heart-beating donor rats results in decreased capillary permeability and increased lung tissue cAMP levels. Pharmacologic augmentation of tissue TAN and cAMP levels may further ameliorate the increased capillary permeability seen in lungs retrieved from non-heart-beating donors.

Adenine Nucleotides↗
PubMed1997

Induction chemoradiotherapy followed by esophagectomy in patients with carcinoma of the esophagus.

BACKGROUND: Induction chemoradiotherapy followed by esophagectomy may provide results superior to those of single-modality treatment in patients with esophageal cancer. The purpose of this study was to review our experience with this approach for esophageal cancer. METHODS: From 1988 to 1996, 166 consecutive patients with esophageal cancer were evaluated; 66 entered a protocol of chemotherapy (5-fluorouracil, cisplatin) concurrent with radiation (45 Gy) followed by esophagectomy. Fifty-four patients completed the protocol. RESULTS: Toxicity associated with induction chemoradiotherapy was minimal. The actuarial survival at 12, 24, and 36 months was 59%, 42%, and 32%, respectively. The pathologic complete response (pCR) rate was 41%, with 12-, 24-, and 36-month survivals of 77%, 50%, and 45%, whereas non-pCR patients had survivals of 46%, 35%, and 23%. The difference in survival between pCR and non-pCR patients was not significant (p = 0.13), but the difference in recurrence-free survival was significant (p = 0.007). CONCLUSIONS: This well-tolerated protocol resulted in a high pCR. Trimodality treatment for esophageal cancer may provide long-term survival in some patients regardless of their pCR status.

Adenocarcinoma↗
PubMed1997

Effect of perfusion pH on rat lung viability of non-heart beating donors.

OBJECTIVE: Non-heart beating donors could be an important source of lungs for transplantation. In prior experiments, trypan blue exclusion was used to assess the percentage of viable lung cells after different intervals following circulatory arrest. In this study, we assessed the importance of the trypan blue perfusate pH because in liver preservation studies, pH of the perfusate appears to be very important with the presence of a 'pH paradox'. METHODS: Forty Sprague-Dawley rats (n = 5 each group) were sacrificed, left at room temperature, and ventilated with 100% O2 (tidal volume 0.01 cc/g, rate 30/min) for 4 or 8 h after death. Lungs were then flushed with 150 cc of trypan blue in Krebs-Heinseleit buffer via the pulmonary artery, then with 150 cc of fixative (2%) paraformaldehyde + 2% gluteraldehyde). The pH of the trypan blue solution was varied from 6.5 to 7.8. Lungs were sectioned, and cell viability was quantified based on exclusion of trypan blue. RESULTS: Longer cadaver time was associated with less viability, but pH had no effect on viability. The results were similar in groups ventilated for the same period of time and then flushed with solutions at different pH (4 h, viability 80-84%; 8 h, viability 68-72%). Over the range investigated, the pH of the trypan blue solution had no impact on lung viability in non-heart beating donors and the lungs did not show the 'pH paradox'. CONCLUSION: Lung tissue is not susceptible to the 'pH paradox' observed in liver preservation studies. Because more than 80% of lung cells are still viable 4 h after death if the lungs are ventilated with 100% O2 during the cadaveric period, retrieval and transplantation of cadaveric lungs may be feasible and might alleviate the paucity of lung donors.

Animals↗
PubMed1997

When does the lung die? Kfc, cell viability, and adenine nucleotide changes in the circulation-arrested rat lung.

Lungs harvested from cadaveric circulation-arrested donors may increase the donor pool for lung transplantation. To determine the degree and time course of ischemia-reperfusion injury, we evaluated the effect of O2 ventilation on capillary permeability [capillary filtration coefficient (Kfc)], cell viability, and total adenine nucleotide (TAN) levels in in situ circulation-arrested rat lungs. Kfc increased with increasing postmortem ischemic time (r = 0.88). Lungs ventilated with O2 1 h postmortem had similar Kfc and wet-to-dry ratios as controls. Nonventilated lungs had threefold (P < 0.05) and sevenfold (P < 0.0001) increases in Kfc at 30 and 60 min postmortem compared with controls. Cell viability decreased in all groups except for 30-min postmortem O2-ventilated lungs. TAN levels decreased with increasing ischemic time, particularly in nonventilated lungs. Loss of adenine nucleotides correlated with increasing Kfc values (r = 0.76). This study indicates that lungs retrieved 1 h postmortem may have normal Kfc with preharvest O2 ventilation. The relationship between Kfc and TAN suggests that vascular permeability may be related to lung TAN levels.

Adenine Nucleotides↗
PubMed1996

Cadaver lungs for transplantation. Effect of ventilation with alveolar gas.

In an effort to increase the donor pool for lung transplantation (LTX), we have demonstrated the feasibility of LTX from circulation-arrested cadavers in a canine LTX model. We hypothesized that ventilation of the cadaver lung with alveolar gas (20% O2, 5% CO2, balance N2) (AG) would be superior to ventilation with 100% oxygen (O2) after circulatory arrest of the donor. Twelve mongrel dogs were intubated, heparinized and euthanized by pentothal injection and ventilated with AG (n=6) or O2 (n=6). Four hours later, donor animals underwent sternotomy, and the lungs were flushed with cold modified Euro-Collins solution, harvested, and stored inflated in ice slush. Left lung allotransplantation was performed, and recipients were made dependent o n the transplanted lung by occlusion of the contralateral bronchus and pulmonary artery. Recipient animals were ventilated with an FiO2 of 0.4 and followed for 8 hr. Total ischemic time was 7.9 hr for both groups. Pulmonary edema developed in all recipients of AG lungs; one recipient survived the 8-hr observation period with poor oxygenation. In contrast, three of six recipients of O2-ventilated lungs survived for 8-hr with excellent gas exchange. Specimens of donor lungs before and after transplant were evaluated histologically utilizing trypan blue exclusion as an indicator of cell viability. At the time of organ retrieval 4 hr after death, 6% of cells were nonviable in the O2-ventilated cadaver lungs. Circulation-arrested cadaver lungs ventilated with 100% O2 prior to organ retrieval have superior pulmonary function after transplant compared with lungs ventilated with AG. Ventilation of cadaver lungs with AG induces pulmonary injury in this model. retrieval of donor lungs from circulation-arrested cadavers has potential for increasing the pulmonary donor pool.

Animals↗
PubMed1996

One hundred consecutive thymectomies for myasthenia gravis.

BACKGROUND: Between June 1997 and November 1993, 100 consecutive thymectomies for myasthenia gravis were performed at University of North Carolina Hospitals in Chapel Hill. METHODS: A consistent, planned protocol involving preoperative, intraoperative, and postoperative care was followed. All thymectomies were performed through a median sternotomy with removal of all visible thymus and perithymic fat in the anterior mediastinum. RESULTS: There was no perioperative mortality or longterm morbidity. Mean postoperative hospital stay was 6.3 days (range, 3 to 18 days). Ninety-six percent of the patients were extubated the day of the operation, and all patients were extubated within 24 hours. Mean postoperative intensive care unit stay was 1.2 days (range, 1 to 4 days). After a mean follow-up of 65 months (range, 1 to 199 months), 78% of all patients are improved by at least one modified Osserman classification when their current status is compared with their worst preoperative disease severity. In fact, 69% of patients with mild disease preoperatively (class I, II, or III maximal severity) are in pharmacologic remission (asymptomatic without regular medication), whereas 29% of patients with severe disease (class IV or V) are in remission (p = 0.0001). CONCLUSIONS: Our programmatic approach to thymectomy through a sternotomy has shown minimal morbidity and mortality. It is beneficial to myasthenics at both ends of the age and severity spectrum.

Adult↗
PubMed1996

Studies of rat lung viability and adenine nucleotide metabolism after death.

BACKGROUND: Prior studies from our laboratory have supported the use of cadaveric lungs for transplantation. In this study we investigated different preservation strategies for lungs retrieved from cadavers 4 hours after circulatory arrest. METHODS: Seventy-two Sprague-Dawley rats were sacrificed and then ventilated with 100% oxygen for 4 hours. The lungs were then flushed with modified Euro-Collins, University of Wisconsin, or Carolina rinse solution, either alone, with prostaglandin E1, or with prostaglandin E1 plus the free radical scavenger dimethylthiourea. After an additional 4-hour cold storage, the left lung was flushed with trypan blue solution to quantify cell viability, whereas the right lung was used to determine wet-to-dry weight ratios and to measure the levels of the adenine nucleotides adenosine triphosphate, adenosine diphosphate, and adenosine monophosphate by high-performance liquid chromatography. RESULTS: Viability was consistently better in the lungs flushed with Carolina rinse solution; these differences were statistically significant compared with those in the corresponding modified Euro-Collins subgroups (p < 0.005). The addition of prostaglandin E1 to all three preservation solutions improved the total adenine nucleotide levels; this increase was statistically significant for the modified Euro-Collins subgroup (p < 0.005). The total adenine nucleotide levels for the University of Wisconsin subgroups were higher than those for the corresponding modified Euro-Collins subgroups. The highest total adenine nucleotide levels were obtained in lungs flushed with Carolina rinse plus prostaglandin E1. Wet-to-dry weight ratios were always significantly lower in the lungs preserved with University of Wisconsin solution (p < 0.05), with a value similar to that of fresh tissue. CONCLUSIONS: The characteristics of the solution used to flush and to store rat cadaveric lungs have an impact on lung viability and adenine nucleotide metabolism. The ideal preservation strategy may allow for lung retrieval from cadavers for safe transplantation.

Adenine Nucleotides↗
PubMed1996

Canine double-lung transplantation with cadaveric donors.

If lungs could be retrieved from cadavers after circulatory arrest, the critical shortage of donors for lung transplantation might be alleviated. To assess gas exchange after transplantation of lungs from cadaveric donors, we performed double-lung transplantation through sequential thoracotomies in 12 dogs. Donors were sacrificed by intravenous pentobarbital injection and then ventilated with 100% oxygen. Lungs were harvested 2 hours (n = 6) or 4 hours (n = 6) after death and flushed with 2 L modified Euro-Collins solution. Recipients underwent sequential right and left lung transplantation; they were then monitored while under anesthesia for 8 hours, with adjustments of the fraction of inspired oxygen. Nine of 12 recipients survived the 8-hour study period. Four of six dogs with cadaveric lungs retrieved 2 hours after death survived; deaths were from pulmonary embolism at 6 hours and pulmonary edema at 2 hours. Five of six dogs with cadaveric lungs retrieved 4 hours after death survived; one died of hypoxia during implantation of the left lung, while dependent on the right lung graft. Postoperative hemodynamic and gas exchange parameters were similar in both groups. Alveolar-arterial oxygen gradient rose significantly compared with baseline 1 hour after transplantation in both groups (462 +/- 60 vs 38 +/- 31 mmHg for 2-hour group, p < 0.0001, and 484 +/- 63 vs 38 +/- 14 mmHg for 4-hour group, p < 0.0002). By 8 hours after operation, the gradients had significantly decreased in both groups (105 +/- 37 mm Hg for 2-hour group and 146 +/- 53 mm Hg for 4-hour group) and were similar to baseline values. Extravascular lung water also rose significantly 1 hour after transplantation (15.7 +/- 2.8 vs 7.9 +/- 0.5 ml/kg for 2-hour group, p < 0.02, and 16.9 +/- 1.2 vs 6.6 +/- 0.4 ml/kg for 4-hour group, p < 0.0001) and decreased gradually during the 8-hour study period. Donor lungs retrieved at 2 and 4 hours postmortem afford similar recipient outcomes. Improvement in alveolar-arterial oxygen gradient and reduction in extravascular lung water during the study period imply that the ischemia-reperfusion injury induced by this model is reversible. If this approach could be safely introduced to clinical practice, substantially more transplant procedures could be performed.

Anesthesia, General↗
PubMed1996

Wegener's granulomatosis mimicking a sternal abscess.

Bone destruction as a manifestation of Wegener's granulomatosis has been reported, but these cases were limited to the head and face. We present a case in which a sternal abscess was the initial manifestation of Wegener's granulomatosis. We believe this is the first reported case of bone destruction due to Wegener's occurring in a location other than the head and face.

Abscess↗
PubMed1996

Seizures in lung transplant recipients.

PURPOSE: We wished to assess organ transplant recipients, who incur a significant risk for seizures. METHOD: We reviewed 85 lung transplants performed in 81 patients at the University of North Carolina hospitals between 1991 and 1994. All patients were reviewed for age, reason for transplant, detailed description of seizures, neurological examination, medications, and laboratory results, including cyclosporine level, EEG, and brain imaging. RESULTS: Eighteen of 81 (22%) patients experienced seizures. Patients aged < 25 years had the greatest risk of seizures and 15 of the 18 patients had cystic fibrosis. Sixteen of the 18 (89%) patients, by history, had partial-onset seizures. Eleven of the 18 (61%) patients had seizures < or = 10 days after initiation of intravenous methylprednisolone for allograft rejection. Two patients had seizures associated with sustained hypertension: 1 of these patients was simultaneously being treated for rejection. Four patients had strokes (1 before transplant) and seizures. Two patients were receiving imipenem. Magnetic resonance imaging (MRI) of the brain demonstrated areas of increased T2 signal in 8 of 9 patients. CONCLUSIONS: Our findings demonstrate multiple etiologies for seizures in our transplant recipients. However, we believe that patients, especially those aged < 25 years, being treated with intravenous methylprednisolone for rejection may be at increased risk of seizures. We hypothesize that the focal loss of blood-brain barrier (BBB) may play a significant role in the development of partial seizures in lung transplant recipients.

Age Factors↗
PubMed1996

Severe osteoporosis before and after lung transplantation.

STUDY OBJECTIVE: Osteoporosis and/or fractures have been reported as a complication of kidney, heart, liver, bone marrow, and, most recently, lung transplantation (LTx). We measured bone mineral density (BMD) before and after LTx to determine the frequency and severity of preoperative and postoperative osteoporosis. PATIENTS AND METHODS: We conducted a cross-sectional study of BMD in 100 patients with various diagnoses before (n = 55) and after (n = 45) LTx. RESULTS: Age-matched mean spine and femoral BMDs were severely depressed before and after LTx placing 45% of the pre-LTx and 73% of the post-LTx patients at or below the fracture threshold (2 SDs below the mean). As expected, patients with cystic fibrosis had lower (p < 0.05) mean spine and femoral BMD than patients with COPD or other lung diseases both before and after LTx. Nevertheless, considerable osteoporosis was present in the patients with COPD and other lung diseases before and after LTx. The best predictors of pre- and post-LTxZ scores were body mass index (r = 0.56 to 0.59, p < 0.001) and cumulative steroid dose/per kilogram (r = 0.49-0.51, p < 0.001), respectively. Osteoporosis has resulted in 3 symptomatic fractures before and 12 after LTx. CONCLUSIONS: Osteoporosis appears to be widespread in patients with end-stage respiratory failure before LTx and LTx, while often life-saving, has an adverse impact on BMD. As patients live longer after LTx, osteoporosis-related fractures may compromise quality of life by causing pain and debilitation.

Adolescent↗