Glycosylation within the cysteine loop and six residues near conserved Cys192/Cys193 are determinants of neuronal bungarotoxin sensitivity on the neuronal nicotinic receptor alpha3 subunit

Neuronal bungarotoxin (NBT) is a highly selective, slowly reversible, competitive antagonist of the alpha3beta2 neuronal nicotinic receptor. Contributions to NBT sensitivity are made by both the alpha3 and beta2 subunits. We used a chimeric alpha subunit to demonstrate that the entire alpha3 contribution lies within sequence segment 84-215. Construction and analysis of a series of mutant alpha3 subunits identified seven amino acid residues (Thr143, Tyr184, Lys185, His186, Ile188, Gln198, Ser203) within this region that contribute to NBT sensitivity. Changing Thr143 to lysine, as in alpha2, resulted in a approximately 1000-fold loss of NBT sensitivity. The effect on NBT sensitivity of changing each of the other six residues ranged from 1.8- to 40.5-fold. More extensive mutagenesis demonstrated that Thr143 serves as part of the consensus sequence for glycosylation at N141, and it is this glycosylation that is the determinant of NBT sensitivity. Only serine could substitute for threonine to maintain full NBT sensitivity, and changing Asn141 to alanine resulted in a approximately 300-fold loss of NBT sensitivity. The chimera alpha2-181-alpha3, containing all identified determinants except the glycosylation site, formed receptors insensitive to 300 nM NBT. Installation of threonine to complete the glycosylation consensus site in this chimera conferred NBT sensitivity only 10-fold less than that of wild-type alpha3beta2. These seven determinants of NBT sensitivity are located in close proximity to a series of conserved residues that are common features of all nicotinic receptor binding sites.

Successful strategies for improving operating room efficiency at academic institutions

In this prospective study, we evaluated the etiology of operating room (OR) delays in an academic institution, examined the impact of multidisciplinary strategies to improve OR efficiency, and established OR timing benchmarks for use in future OR efficiency studies. OR times and delay etiologies were collected for 94 cases during the initial phase of the study. Timing data and delay etiologies were analyzed, and 2 wk of multidisciplinary OR efficiency awareness education was conducted for the nursing, surgical, and anesthesia staff. After the education period, timing data were collected from 1787 cases, and monthly reports listing individual case delays and timing data were sent to the Chiefs of Service. For the first case of the day, patient in room, anesthesia ready, surgical preparation start, and procedure start time were significantly earlier (P < 0.01) in the posteducation period compared with the preeducation period, and the procedure start time for the first case of the day occurred, on average, 22 min earlier than all other procedures. For all cases combined, turnover time decreased, on average, by 16 min. Unavailability of surgeons, anesthesiologists, and residents decreased significantly (P < 0.05) as causes of OR delays. Anesthesia induction times were consistently longer for the vascular and cardiothoracic services, whereas surgical preparation time was increased for the neurosurgical and orthopedic services (P < 0.05). Identification of the etiology of OR inefficiency, combined with multidisciplinary awareness training and personal accountability, can improve OR efficiency. The time savings realized are probably most cost-effective when combined with more flexible OR staffing and improved OR scheduling.

IMPLICATIONS

We achieved significant improvements in operating room efficiency by analyzing operating room data on causes of delays, devising strategies for minimizing the most common delays, and subsequently measuring delay data. Personal accountability, streamlining of procedures, interdisciplinary team work, and accurate data collection were all important contributors to improved efficiency.

Differential inhibition by alpha-conotoxin-MII of the nicotinic stimulation of [3H]dopamine release from rat striatal synaptosomes and slices

The presynaptic nicotinic modulation of dopamine release from striatal nerve terminals is well established, but the subtype(s) of neuronal nicotinic acetylcholine receptor (nAChR) underlying this response has not been identified. Recently, alpha-conotoxin-MII has been reported to inhibit potently and selectively the rat alpha3beta2 combination of nAChR subunits. Here we have synthesised the peptide, confirmed its specificity, and examined its effect on the (+/-)-anatoxin-a-evoked release of [3H]dopamine from rat striatal synaptosomes and slices. Alpha-conotoxin-MII (112 nM) completely blocked acetylcholine-evoked currents of alpha3beta2 nAChRs expressed in Xenopus oocytes (IC50 = 8.0 +/- 1.1 nM). Pairwise combinations of other nicotinic subunits were not blocked by 112 nM alpha-conotoxin-MII. On perfused striatal synaptosomes and slices, alpha-conotoxin-MII dose-dependently inhibited [3H]dopamine release evoked by 1 microM (+/-)-anatoxin-a with IC50 values of 24.3 +/- 2.9 and 17.3 +/- 0.1 nM, respectively. The dose-response curve was shifted to the right with increasing agonist concentrations. However, the maximal inhibition of responses achieved by alpha-conotoxin-MII (112 nM) was 44.9 +/- 5.4% for synaptosomes and 25.0 +/- 4.1% for slices, compared with an inhibition by 10 microM mecamylamine of 77.9 +/- 3.7 and 88.0 +/- 2.1%, respectively. These results suggest the presence of presynaptic alpha3beta2-like nAChRs on striatal dopaminergic terminals, but the incomplete block of (+/-)-anatoxin-a-evoked [3H]dopamine release by alpha-conotoxin-MII also supports the participation of nAChRs composed of other subunits. The lower inhibition found in slices is consistent with an additional indirect nicotinic stimulation of dopamine release via an alpha-conotoxin-MII-insensitive nAChR.

Large-needle core biopsy: nonmalignant breast abnormalities evaluated with surgical excision or repeat core biopsy

PURPOSE

To classify lesions initially considered nonmalignant at large-needle core biopsy that were subsequently surgically excised or sampled at repeat biopsy.

MATERIALS AND METHODS

From August 1, 1991, to December 31, 1996, 1,032 breast abnormalities (214 malignant and 818 nonmalignant lesions) were sampled at large-needle core biopsy. Of the nonmalignant lesions, 112 (14%) abnormalities were studied. Twenty-four abnormalities were subsequently excised because of discordant imaging and pathologic findings; 41 may have been missed at biopsy (25 were surgically excised, and 16 were sampled at repeat biopsy); 40 were surgically excised as recommended by the pathologist; and seven were excised for other indications.

RESULTS

None of 24 abnormalities excised because of discordant findings was malignant. Among the 41 possibly missed lesions, infiltrating ductal carcinoma was found in one lesion that was removed surgically and in one sampled at repeat biopsy. Among the 40 lesions recommended for excision by the pathologist, 16 malignancies were found (ductal carcinoma in situ, 11; infiltrating ductal carcinoma, three; phyllodes tumor, two). None of the remaining seven lesions was malignant.

CONCLUSION

Correlation of the technical quality of the biopsy, imaging features, and pathologic findings resulted in 96 surgical excisions and 16 repeat biopsies of lesions initially considered nonmalignant. Eighteen additional malignancies were identified.

Medical treatment and discharge planning for a patient with a borderline personality: a multidisciplinary challenge

This case study discusses a patient with substantial medical problems whose hospital course was further complicated by her borderline personality disorder. Difficulties related to this patient's hospital course included noncompliant, manipulative, and self-injurious behaviors as well as obstacles encountered during discharge planning. Given the impact these maladaptive behaviors can have on the efficacy and cost of treatment, in addition to ward operations and staff morale, this case study highlights the importance of a timely recognition of dysfunctional personality traits. In addition, the establishment of a multidisciplinary treatment team that used a "whole person" approach was beneficial in overcoming many of the obstacles hindering her recovery and also proved useful in dealing with the managed health care system.

Continuous intrathecal meperidine via an implantable infusion pump for chronic, nonmalignant pain

OBJECTIVE

To report a continuous infusion of intrathecal meperidine via an implanted infusion pump for nonmalignant, chronic pain.

CASE SUMMARY

A 69-year-old white woman had chronic, nonmalignant low-back pain and bilateral leg pain. Multiple drug therapies and other interventional techniques had failed. The patient achieved significant pain relief by a continuous infusion of intrathecal meperidine via an implanted infusion pump.

DISCUSSION

To our knowledge, this is the first report of meperidine administered intrathecally by continuous infusion. Continuous infusion of intrathecal and epidural opiates by implanted infusion pumps is becoming more widely recognized as an alternative treatment for patients with chronic, benign pain. Epidural and intrathecal meperidine is an effective analgesic for short-term surgical procedures. Data reporting effective relief and safety with continuous intrathecal meperidine remain limited.

CONCLUSIONS

Continuous intrathecal meperidine via an implantable infusion pump may be an effective alternative in the treatment of chronic pain.

Reducing cardiac surgical trauma: the minimally invasive direct coronary artery bypass

BACKGROUND

The concept of minimal surgical trauma is revolutionizing many surgical subspecialties, including cardiac surgery. Coronary artery revascularization can now be accomplished either thoracoscopically or through a small thoracotomy, sternotomy, or epigastric incision, with or without cardiopulmonary bypass (CPB).

METHODS

The current literature was reviewed with regard to patient selection criteria for coronary artery bypass grafting (CABG) without CPB, indications for minimally invasive direct coronary artery bypass (MIDCAB), surgical and anesthetic technique, and outcome.

RESULTS

The MIDCAB is largely used in cases of single or double vessel disease. The procedure is done either thoracoscopically or under direct vision through a small incision rather than standard sternotomy. In non-CPB cases, the heart is pharmacologically manipulated to create a quiet operative field. Patients may be extubated and become ambulatory shortly after surgery and be discharged within a few days.

CONCLUSIONS

The MIDCAB avoids median sternotomy and, in many cases, CPB. MIDCAB may prove to play a prominent role in management of coronary artery disease in the future.

Stereotactic breast biopsy of clustered microcalcifications with a directional, vacuum-assisted device

The success rate with the traditional 14-gauge, core-biopsy, multiple-pass technique was compared with that of a directional vacuum-assisted device in sampling calcification clusters in the breast. Of the 130 focal calcification clusters sampled with the multiple-pass technique, 12 clusters (9.2%) had no particles depicted on radiographs of the specimen. Specimens from all 106 (100%) clusters sampled with the directional, vacuum-assisted instrument contained calcifications at radiography. The directional, vacuum-assisted device improved the ability to percutaneously sample breast calcifications.

Flexible DNA: genetically unstable CTG.CAG and CGG.CCG from human hereditary neuromuscular disease genes

The properties of duplex CTG.CAG and CGG.CCG, which are involved in the etiology of several hereditary neurodegenerative diseases, were investigated by a variety of methods, including circularization kinetics, apparent helical repeat determination, and polyacrylamide gel electrophoresis. The bending moduli were 1.13 x 10(-19) erg.cm for CTG and 1.27 x 10(-19) erg.cm for CGG, approximately 40% less than for random B-DNA. Also, the persistence lengths of the triplet repeat sequences were approximately 60% the value for random B-DNA. However, the torsional moduli and the helical repeats were 2.3 x 10(-19) erg.cm and 10.4 base pairs (bp)/turn for CTG and 2.4 x 10(-19) erg.cm and 10.3 bp/turn for CGG, respectively, all within the range for random B-DNA. Determination of the apparent helical repeat by the band shift assay indicated that the writhe of the repeats was different from that of random B-DNA. In addition, molecules of 224-245 bp in length (64-71 triplet repeats) were able to form topological isomers upon cyclization. The low bending moduli are consistent with predictions from crystallographic variations in slide, roll, and tilt. No unpaired bases or non-B-DNA structures could be detected by chemical and enzymatic probe analyses, two-dimensional agarose gel electrophoresis, and immunological studies. Hence, CTG and CGG are more flexible and highly writhed than random B-DNA and thus would be expected to act as sinks for the accumulation of superhelical density.

Ribonuclease P RNA: models of the 15/16 bulge from Escherichia coli and the P15 stem loop of Bacillus subtilis

The Escherichia coli ribonuclease P RNA 15/16 internal bulge loop and the Bacillus subtilis P15 stem loop are important substrate binding sites for the CCA-3' terminus of pre-tRNA. Models of E. coli 15/16 bulge loop and the B. subtilis P15 stem loop have been constructed using MC-SYM, a constraint satisfaction program. The models use covariation analysis data for suggesting initial base pairings, chemical probing, and protection/modification results to determine particular pairing orientations, and mutational experimental analysis data for tRNA-RNase P RNA contacts. The structures from E. coli and B. subtilis, although different in secondary structure, have similar sequence and function. Using MC-SYM, we are able to illustrate how the 3' end of the pre-tRNA is able to interact with this segment of the catalytic RNase P RNA. In addition, we propose additional hydrogen bonding between A76 in the 3' terminus of the tRNA and the 15/16 region of E. coli and to the loop of B. subtilis.

Slipped structures in DNA triplet repeat sequences: entropic contributions to genetic instabilities

Slipped DNA structures can occur in sequences with direct repeats. DNA triplet repeats, particularly (CTG)n, (CGC)n, and (GAA)n, are known to be associated with several neurological diseases. Slippage is probably the cause of expansion of the number of repeats, a process called dynamic mutation, which is known to be the cause of the diseased state. Here it is shown that the conformational entropy associated with slippage is more destabilizing for long direct repeats (300-1000 base pairs) than shorter runs (10-30 base pairs), by about 2 kcal/mol. This contributes to the greater instability of longer sequences. Entropic considerations also favor the formation of simple bulges, rather than hairpin structures. A model is presented for dynamic mutations, and experimentally testable predictions are made that will allow the model to be tested.

Determinants of specificity for alpha-conotoxin MII on alpha3beta2 neuronal nicotinic receptors

The competitive antagonist alpha-conotoxin-MII (alpha-CTx-MII) is highly selective for the alpha3beta2 neuronal nicotinic receptor. Other receptor subunit combinations (alpha2beta2, alpha4beta2, alpha3beta4) are >200-fold less sensitive to blockade by this toxin. Using chimeric and mutant subunits, we identified amino acid residues of alpha3 and beta2 that participate in determination of alpha-CTx-MII sensitivity. Chimeric alpha subunits, constructed from the alpha3 and alpha4 subunits, as well as from the alpha3 and alpha2 subunits, were expressed in combination with the beta2 subunit in Xenopus laevis oocytes. Chimeric beta subunits, formed from the beta2 and beta4 subunits, were expressed in combination with alpha3. Determinants of alpha-CTx-MII sensitivity on alpha3 were found to be within sequence segments 121-181 and 181-195. The 181-195 segment accounted for approximately half the difference in toxin sensitivity between receptors formed by alpha2 and alpha3. When this sequence of alpha2 was replaced with the corresponding alpha3 sequence, the resulting chimera formed receptors only 26-fold less sensitive to alpha-CTx-MII than alpha3beta2. Site-directed mutagenesis within segment 181-195 demonstrated that Lys185 and Ile188 are critical in determination of sensitivity to toxin blockade. Determinants of alpha-CTx-MII sensitivity on beta2 were mapped to sequence segments 1-54, 54-63, and 63-80. Site-directed mutagenesis within segment 54-63 of beta2 demonstrated that Thr59 is important in determining alpha-CTx-MII sensitivity.

The effect of bupivacaine skull block on the hemodynamic response to craniotomy

The placement of pointed cranial pins into the periosteum is a recognized acute noxious stimulation during intracranial surgery which can result in sudden increases in blood pressure and heart rate, causing increases in intracranial pressure. A skull block (blockade of the nerves that innervate the scalp, including the greater and lesser occipital nerves, the supraorbital and supratrochlear nerves, the auriculotemporal nerves, and the greater auricular nerves) may be effective in reducing hypertension and tachycardia. Twenty-one patients were allocated in a prospective, double-blind fashion to a control group or a bupivacaine group. After a standardized induction and 5 min prior to head pinning, a skull block was performed. Patients in the control group received a skull block of normal saline, while the bupivacaine group received a skull block with 0.5% bupivacaine. Systolic (SAP), diastolic (DAP), mean arterial pressure (MAP), heart rate (HR), and end-tidal isoflurane were recorded at the following times: 5 min after the induction of anesthesia, during performance of the skull block, during head pinning, and 5 min after head pinning. Significant increases in SAP of 40 +/- 6 mm Hg, DAP of 30 +/- 5 mm Hg, MAP of 32 +/- 6 mm Hg, and HR of 22 +/- 5 bpm occurred during head pinning in the control group, while remaining unchanged in the bupivacaine group. These results demonstrate that a skull block using 0.5% bupivacaine successfully blunts the hemodynamic response to head pinning.

Multiple determinants of dihydro-beta-erythroidine sensitivity on rat neuronal nicotinic receptor alpha subunits

Neuronal nicotinic acetylcholine receptors are differentially sensitive to blockade by the competitive antagonist dihydro-beta-erythroidine. Both alpha and beta subunits participate in determining sensitivity to this antagonist. The alpha subunit contribution to dihydro-beta-erythroidine sensitivity is illustrated by comparing the alpha 4 beta 4 receptor and the alpha 3 beta 4 receptor, which differ in sensitivity to dihydro-beta-erythroidine by approximately 120-fold. IC50 values for blocking alpha 4 beta 4 and alpha 3 beta 4, responding to EC20 concentrations of acetylcholine, were 0.19 +/- 0.06 and 23.1 +/- 10.2 microM, respectively. To map the sequence segments responsible for this difference, we constructed a series of chimeric alpha subunits containing portions of the alpha 4 and alpha 3 subunits. These chimeras were coexpressed with beta 4, allowing pharmacological characterization. We found determinants of dihydro-beta-erythroidine sensitivity to be distributed throughout the N-terminal extracellular domain of the alpha subunit. These determinants were localized to sequence segments 1-94, 94-152, and 195-215. Loss of determinants within segment 1-94 had the largest effect, decreasing dihydro-beta-erythroidine sensitivity by 4.3-fold.

Management of cancer pain

Pain is often the first symptom of cancer. Pain and fear of pain are concerns of most cancer patients and their families. The therapeutic options available to control pain are numerous, allowing practitioners to better individualize treatment. We present an overview of the pathophysiology of cancer pain, the current theories of pharmacologic opioid management, advantages of adjuvant drugs, and the range of invasive and noninvasive procedures that practitioners can offer their patients who have cancer-related pain.