Keith Baxter

Blockade by ifenprodil of high voltage-activated Ca2+ channels in rat and mouse cultured hippocampal pyramidal neurones: comparison with N-methyl-D-aspartate receptor antagonist actions

1 The block by ifenprodil of voltage‐activated Ca2+ channels was investigated on increases in intracellular free calcium concentration ([Ca2+]i) evoked by 50 mm K+ (high‐[K+]o) in Fura‐2‐loaded rat hippocampal pyramidal neurones in culture and on currents carried by Ba2+ ions (IBa) through Ca2+ channels in mouse cultured hippocampal neurones under whole‐cell voltage‐clamp. The effects of ifenprodil on voltage‐activated Ca2+ channels were compared with its antagonist actions on N‐methyl‐D‐aspartate‐ (NMDA) evoked responses in the same neuronal preparations. 2 Rises in [Ca2+]i evoked by transient exposure to high‐[K+]o in our preparation of rat cultured hippocampal pyramidal neurones are mediated predominantly by Ca2+ flux through nifedipine‐sensitive Ca2+ channels, with smaller contributions from nifedipine‐resistant, ω‐conotoxin GVIA‐sensitive Ca2+ channels and Ca2+ channels sensitive to crude funnel‐web spider venom (Church et al., 1994). Ifenprodil (0.1 −200 μm) reversibly attenuated high‐[K+]o‐evoked rises in [Ca2+]i with an IC50 value of 17 ± 3 μm, compared with an IC50 value of 0.7 ± 0.1 μm for the reduction of rises in [Ca2+]i evoked by 20 μm NMDA. Tested in the presence of nifedipine 10 μm, ifenprodil (1–50 μm) produced a concentration‐dependent reduction of the dihydropyridine‐resistant high‐[K+]o‐evoked rise in [Ca2+]i with an IC50 value of 13 ± 4 μm. The results suggest that ifenprodil blocks Ca2+ flux through multiple subtypes of high voltage‐activated Ca2+ channels. 3 Application of the polyamine, spermine (0.25‐5 μm), produced a concentration‐dependent reduction of rises in [Ca2+]i evoked by high‐[K+]o. The antagonist effects of ifenprodil 20 μm on high‐[K+]o‐evoked rises in [Ca2+]i were attenuated by spermine 0.25 mm but not by putrescine 1 or 5 mm. In contrast, spermine 0.1 mm increased rises in [Ca2+]i evoked by NMDA and enhanced the ifenprodil (5 μm) block of NMDA‐evoked rises in [Ca2+]i. 4 Similar results were obtained in mouse cultured hippocampal pyramidal neurones under whole‐cell voltage‐clamp. Ifenprodil attenuated both the peak and delayed whole‐cell IBa with an IC50 value of 18 ± 2 μ, whilst it attenuated steady‐state NMDA‐evoked currents with an IC50 of 0.8 ± 0.2 μm. Block of IBa by ifenprodil 10 μm was rapid in onset, fully reversible and occurred without change in the current‐voltage characteristics of IBa. The ifenprodil block of IBa was enhanced on membrane depolarization and was weakly dependent on the frequency of current activation. Spermine 0.1 mm potentiated control NMDA‐evoked currents but attenuated IBa. In agreement with the microspectrofluorimetric studies, co‐application of spermine produced a small enhancement of the inhibitory effect of ifenprodil 10 μm on NMDA‐evoked responses whereas the reduction of IBa by ifenprodil 10 μm in the presence of spermine was less than expected if the inhibitory effects of ifenprodil and spermine on IBa were simply additive. 5 The results indicate that ifenprodil blocks high voltage‐activated Ca2+ channels in rat and mouse cultured hippocampal pyramidal neurones. Although the Ca2+ channel blocking actions of ifenprodil are observed at higher concentrations than those associated with NMDA antagonist activity, Ca2+ channel blockade may contribute, at least in part, to the established neuroprotective and anticonvulsant properties of the compound.

pH modulation of Ca2+ responses and a Ca2+-dependent K+ channel in cultured rat hippocampal neurones

1 The effects of changes in extra‐ and intracellular pH (pHo and pHi, respectively) on depolarization‐evoked rises in intracellular free Ca2+ concentration ([Ca2+]i) and the activity of a Ca2+‐dependent K+ channel were investigated in cultured fetal rat hippocampal neurones. 2 In neurones loaded with 2′,7′‐bis‐(2‐carboxyethyl)‐5‐(and ‐6)‐carboxyfluorescein (BCECF), changes in pHo evoked changes in pHi. At room temperature, the ratio ΔpHi : ΔpHo (the slope of the regression line relating pHi to pHo) was 0·37 under HCO3−/CO2‐buffered conditions and 0·45 under Hepes‐buffered conditions; corresponding values at 37 °C were 0·71 and 0·79, respectively. The measurements of changes in pHi evoked by changes in pHo were employed in subsequent experiments to correct for the effects of changes in pHi on the Kd of fura‐2 for Ca2+. 3 In fura‐2‐loaded neurones, rises in [Ca2+]i evoked by transient exposure to 50 mM K+ were reduced and enhanced during perfusion with acidic and alkaline media, respectively, compared with control responses at pHo 7·3. Fifty percent inhibition of high‐[K+]o‐evoked rises in [Ca2+]i corresponded to pHo 7·23. In the presence of 10 μM nifedipine, 50 % inhibition of high‐[K+]o‐evoked responses corresponded to pHo 7·20, compared with a pHo of 7·31 for 50 % inhibition of [Ca2+]i transients evoked by N‐methyl‐D‐aspartate. 4 Changes in pHi at a constant pHo were evoked by exposing neurones to weak acids or bases and quantified in BCECF‐loaded cells. Following pH‐dependent corrections for the Kd of fura‐2 for Ca2+, rises in [Ca2+]i evoked by high‐[K+]o in fura‐2‐loaded cells were found to be affected only marginally by changes in pHi. When changes in pHi similar to those observed during the application of weak acids or bases were elicited by changing pHo, reductions in pH inhibited rises in [Ca2+]i evoked by 50 mM K+ whereas increases in pH enhanced them. 5 The effects of changes in pH on the kinetic properties of a BK‐type Ca2+‐dependent K+ channel were investigated. In inside‐out patches excised from neurones in sister cultures to those used in the microspectrofluorimetric studies, with internal [Ca2+] at 20 μM, channel openings at an internal pH of 6·7 were generally absent whereas at pH 7·3 (or 7·8) the open probability was high. In contrast, channel activity in outside‐out patches was not affected by reducing the pH of the bath (external) solution from 7·3 to 6·7. In inside‐out patches with internal [Ca2+] at 0·7 μM, a separate protocol was applied to generate transient activation of the channel at a potential of 0 mV following a step from a holding level of ‐80 mV. In this case open probabilities were 0·81 (at pH 7·8), 0·57 (pH 7·3), 0·19 (pH 7·0) and 0·04 (pH 6·7). Channel conductance was not affected by changes in internal pH. 6 The results indicate that, in fetal rat hippocampal neurones, depolarization‐evoked rises in [Ca2+]i mediated by the influx of Ca2+ ions through dihydropyridine‐sensitive and ‐resistant voltage‐activated Ca2+ channels are modulated by changes in pHo. The effects of pHo cannot be accounted for by changes in pHi consequent upon changes in pHo. However, changes in pHi affect the unitary properties of a Ca2+‐dependent K+ channel. The results support the notion that pHo and/or pHi transients may serve a modulatory role in neuronal function.

Intra-abdominal complications after surgical repair of small bowel injuries: an international review.

BACKGROUND The ideal method of repairing serious small bowel injuries remains unknown. Prior reports suggest a higher rate of enteric anastomotic-related complications (EACs) with stapled posttraumatic bowel anastomosis but did not specifically focus on the small bowel or clarify fully the actual anastomotic construction. METHODS This was a retrospective review of patients requiring surgical repair of small bowel perforations at a Level I urban American center (Detroit Receiving Hospital [DRH]) and a Canadian provincial trauma center (Vancouver Hospital and Health Sciences Center [VHHSC]). All patients requiring a primary repair and/or resection were included. Anastomoses were hand-sewn, stapled, or combined stapling and sewing with mucosal inversion. Leaks, anastomotic fistulae, and intra-abdominal abscesses were considered specific EACs. A sample size of 53 per group was obtained to detect a 17% difference at alpha = 0.05 (one-sided) and beta = 0.2. RESULTS Full-thickness small bowel injuries were repaired in 232 patients (DRH, 165; VHHSC, 67). Injuries were penetrating at DRH (91.5%) and blunt at VHHSC (65.7%). Anastomotic repairs in 127 patients (158 anastomotic repairs [DRH, 113; VHHSC, 55]) were 64 (40.5%) stapled, 38 (24.1%) hand-sewn, and 56 (35.4%) combined. Also, 105 patients had 349 primary closures of an injury. Overall, there were 24 EACs. After anastomosis, there were 11 intra-abdominal abscesses: 6 after stapling, 3 after being sewn, and 2 after a combined construction. There were four small bowel anastomotic fistulae: three after stapled-only anastomosis and one after hand-sewing. After enteroenterostomy, the EAC rate was 10.2% per patient, or 8.4% per anastomosis. After primary repairs, one patient had an anastomotic fistula, which closed spontaneously, and 11 had intra-abdominal abscesses, yielding an EAC rate of 10.6% per patient or 3.4% per repair. A primary repair was significantly less likely to be associated with an EAC than any anastomosis (p = 0.035). No method of anastomosis was statistically safer in relation to EACs, whether analyzed by patient, by anastomosis, or by considering primarily either the use of a linear stapler or the principle of inverting the mucosal approximation. Only damage control procedures and associated pancreaticoduodenal injuries were identified as statistically significant predictors using multiple logistic regression analysis. CONCLUSION Anastomotic complications after enteroenterostomy or primary repair for trauma are uncommon regardless of the technique, but surgeons must be especially cautious during or after damage control. Primary repairs are desirable, but when anastomosis is unavoidable, the method of repair should reflect that with which the surgeon is the most comfortable.

A Practical Guide to Magnetic Resonance Vascular Imaging: Techniques and Applications

Magnetic resonance angiography is a technique used to image both central and peripheral arteries using contrast and noncontrast techniques. These techniques are similar in that a bright signal, which appears white within blood vessels, is generated and the background tissues, veins, and stationary tissues are dark. This allows for assessment of anatomy and vascular disease. Extracellular gadolinium-based contrast agents allow for excellent visualization of both central and peripheral arteries. Acquiring images during first pass is required for high-contrast images within arteries, thereby limiting contamination with contrast enhancement of veins and soft tissue. Contrast-enhanced techniques using time-resolved angiography and blood pool contrast agents minimize this temporal limitation. Noncontrast techniques eliminate the uncommon but potentially fatal complications associated with gadolinium contrast agents, such as nephrogenic systemic fibrosis. These techniques including phase contrast and time-of-flight sequences have inferior contrast resolution compared with contrast-enhanced techniques and are susceptible to artifacts, which can limit interpretation. The advantage, however, is the ability to assess vascular disease in patients with severe renal failure without the added risks of gadolinium contrast media. The aim of this review is to outline the different techniques available for imaging both the arterial and venous systems, their advantages and disadvantages, and the indications in vascular disease.

Using a Chimney to Make a Sandwich: Salvage of a Multibranched Thoracoabdominal Aortic Endograft with a Type IIIb Endoleak

BACKGROUND The advent of branched and fenestrated aortic endografts has facilitated the treatment of increasingly complex aortic pathology. The management of complications and endoleaks involving the branches and fenestrations of these grafts represents an increasingly significant clinical and technical challenge. METHODS A 79-year-old woman developed a rare type IIIb endoleak from a tear in the graft fabric immediately posterior to the celiac axis branch 3 years after the placement of an off-the-shelf branched endograft for a type II thoracoabdominal aortic aneurysm. The patient presented urgently with abdominal pain and a maximal aneurysm diameter of 15.3 cm. RESULTS The operative plan was to create a chimney graft completely within the original branched endograft to cover the defect and maintain celiac branch flow. The celiac trunk was accessed from a left axillary approach and access for the main endograft body was achieved via the left femoral artery. Two balloon-expandable covered stents were deployed from the celiac branch extending into the main endograft as a chimney and molded to 2 aortic extension cuffs to cover the fabric defect. The resultant configuration was a modified-sandwich graft within the original stent graft and resulted in successful exclusion of the endoleak. Postoperative imaging at 1, 6, and 12 months has demonstrated continued patency of the celiac trunk, no further endoleak, and a 16-mm reduction in aneurysm size. CONCLUSIONS The chimney technique was successfully applied as an endovascular option to salvage a multibranched endograft with a significant and anatomically unfavorable defect. Careful follow-up and additional clinical study are required to clarify the role of off-the-shelf solutions in complex endoleak management.

An age-based comparison of fistula location, patency, and maturation for elderly renal failure patients

Objective: Current Kidney Disease Outcomes Quality Initiative guidelines do not incorporate age in determining autogenous arteriovenous hemodialysis access placement, and the optimal initial configuration in elderly patients remains controversial. We compared patency, maturation, survival, and complications between several age cohorts (<65 years, 65‐79 years, >80 years) to determine whether protocols should be modified to account for advanced age. Methods: All patients at two teaching hospitals undergoing a first autogenous arteriovenous access creation in either arm between 2007 and 2013 were retrospectively analyzed from a prospectively maintained database. Kaplan‐Meier survival and Cox hazards models were used to compare access patency and risk factors for failure. Results: There were 941 autogenous arteriovenous accesses (median follow‐up, 23 months; range, 0‐89 months) eligible for inclusion; 152 (15.3%) accesses were created in those >80 years, 397 (42.2%) in those 65 to 79 years, and 392 (41.8%) in those <65 years. Primary patencies in patients >80 years, 65 to 79 years, and <65 years were 40% ± 4%, 38% ± 3%, and 51% ± 3% at 12 months and 12% ± 5%, 13% ± 3%, and 27% ± 3% at 36 months (P < .001). Primary assisted patencies were 72% ± 4%, 70% ± 2%, and 78% ± 2% at 12 months and 52% ± 5%, 52% ± 3%, and 67% ± 3% at 36 months (P < .001). Secondary patencies were 72% ± 4%, 71% ± 2%, and 79% ± 2% at 12 months and 54% ± 5%, 55% ± 3%, and 72% ± 3% at 36 months (P < .001). Radiocephalic patencies were lowest among older cohorts; in those >80 years, 65 to 79 years, and <65 years, they were 65% ± 7%, 67% ± 4%, and 77% ± 3% at 12 months and 41% ± 8%, 51% ± 5%, and 68% ± 4% at 36 months (P = .019). Secondary brachiocephalic access patencies in these cohorts were 78% ± 5%, 80% ± 3%, and 82% ± 3% at 12 months and 68% ± 7%, 66% ± 5%, and 77% ± 4% at 36 months (P = .206). Both the age groups 65 to 79 years and >80 years demonstrated superior brachiocephalic vs radiocephalic secondary patencies (P = .048 and P = .015, respectively); however, no differences between configuration and secondary patency were observed within the cohort <65 years. Radiocephalic access maturation failure at 12 and 24 months was 25% ± 3% and 29% ± 4% in those <65 years, 32% ± 3% and 39% ± 4% in those 65 to 79 years, and 40% ± 7% and 48% ± 8% in those >80 years (P = .006). Brachiocephalic access maturation failures were 17% ± 3% and 20% ± 3% at 12 and 24 months in those <65 years, 21% ± 3% and 25% ± 4% in those 65 to 79 years, and 18% ± 5% and 21% ± 5% in those >80 years (P = .740). On multivariate analysis, coronary disease, female sex, previous ipsilateral or bilateral catheters, radiocephalic configuration, and age >65 years were associated with secondary patency loss. Conclusions: Patients aged 65 to 79 years and >80 years had inferior primary, primary assisted, and secondary patency and maturation compared with those <65 years. When stratified by configuration, radiocephalic accesses demonstrated lower patency and maturation compared with brachiocephalic accesses for patients aged 65 to 79 years and >80 years and were an independent predictor of secondary patency loss.

Endovascular Repair of Extent II-IV Thoracoabdominal Aortic Aneurysms

Two type II endoleaks were present but did not require reintervention. The composite outcome was achieved in 83% of cases (5 of 6). Conclusions: Off-the-shelf bifurcated-bifurcated aneurysm repairs for aortoiliac aneurysm disease can be safely and efficiently performed in a majority of cases to maintain IIA perfusion and to avoid pelvic ischemic complications. Attention should be directed at purpose-built bridging stents for the general purpose of branch vessel preservation. Comparison to historical controls with IIA embolization is warranted.