Electrophysiological Characterization of a Novel Conotoxin That Blocks Molluscan Sodium Channels

A novel peptide toxin, PnIVB, isolated from the venom of Conus pennaceus blocks voltage-gated sodium current in Aplysia neurons. Complete blockade is obtained at a PnIVB concentration of 80±2.2 nM and 50% blockade at 16±0.86 nM. The potency of PnIVB in blocking Aplysia sodium current is four orders of magnitude larger than that of tetrodotoxin. The toxin has no paralytic activity when injected into fish. The rapid blockade of sodium current by PnIVB is not associated with a change in the activation or inactivation kinetics of the current, or with the reversal potential. Sodium current blockade is reversible after a 30 min wash with 50 times the bath volume. The novel conotoxin PnlVB can be used as a powerful tool for mollusc neurobiological research and as a molecular probe to explore the structure-function relations of voltage-gated sodium channel subtypes.     

Receptor-mediated toxicity of pahutoxin, a marine trunkfish surfactant.

Pahutoxin (PHN, choline chloride ester of 3-acetoxypalmitic acid) is a natural fish-killing (ichthyotoxic) agent derived from the defensive secretions of trunkfish. In spite of its obvious structural resemblance to synthetic cationic long-chain quaternary ammonium detergents, we show that PHN's action does not rely on its surfactant properties and is in fact, receptor-mediated. The above conclusion is supported by the following data: 1. Ichthyotoxicity is not related to its detergency or surfactivity, as indicated by the fact that the lethal concentration is about 1.5 orders of magnitude below its critical micelle concentration value (69 microM) and its liposomal/seawater partition coefficient is low (62-85); 2. The trunkfish is tolerant to its own pahutoxin; 3. Ichthyotoxicity occurs only upon application to the surrounding water, suggesting the existence of externally located receptors; 4. The receptor hypothesis was supported by the aid of equilibrium saturation binding assays revealing the presence of specific binding sites to PHN on the fish gill membranes; 5. The PHN tolerant trunkfish was shown to be devoid of PHN-binding sites. Some chemo-ecological, and environmental implications are discussed.     

Initial experience of videocapsule endoscopy for diagnosing small-bowel tumors in patients with GI polyposis syndromes

BACKGROUND: Small-bowel tumors frequently occur in familial adenomatous polyposis and other GI polyposis syndromes. These tumors are difficult to detect with conventional techniques. Our aim was to assess the utility of videocapsule endoscopy in the detection of small-bowel tumors in this setting. METHODS: We examined 19 familial adenomatous polyposis patients and 3 patients with either Peutz-Jeghers syndrome, hyperplastic polyposis, or Cowden disease. OBSERVATIONS: Prevalence of small-bowel polyps on videocapsule endoscopy was 59% in all patients, 52.6% in familial adenomatous polyposis patients, and 75% in a subgroup of familial adenomatous polyposis patients with exon 15 mutations. Videocapsule endoscopy was safe and well tolerated in all patients. CONCLUSIONS: Videocapsule endoscopy has a high yield in detecting small-bowel tumors in patients with GI polyposis syndromes. It may be especially indicated in familial adenomatous polyposis patients with the aggressive phenotype of the disease, e.g., mutations in exon 15.     

Motor cortical representation of position and velocity during reaching

This study examines motor cortical representation of hand position and its relationship to the representation of hand velocity during reaching movements. In all, 978 motor cortical neurons were recorded from the proximal arm area of rostral motor cortex. The results demonstrate that position and velocity are simultaneously encoded by single motor cortical neurons in an additive fashion and that the relative weights of the position and velocity signals change dynamically during reaching. The two variables--hand position and hand velocity--are highly correlated in the standard center-out reaching task. A new reaching task (standard reaching) is introduced to minimize these correlations. Likewise, a new decoding method (indirect OLE) was developed to analyze the data by simultaneously decoding both three-dimensional (3D) hand position and 3D hand velocity from correlated neural activity. This method shows that, on average, the reconstructed velocity led the actual hand velocity by 122 ms, whereas the reconstructed position signal led the actual hand position by 81 ms.     

Prevention of experimental antiphospholipid syndrome and endothelial cell activation by synthetic peptides

Antiphospholipid syndrome (APS) is characterized by recurrent fetal loss, repeated thromboembolic phenomena, and thrombocytopenia. The syndrome is believed to be caused by antiphospholipid beta-2-glycoprotein-I (beta2GPI)-dependent Abs or anti-beta2GPI Abs by themselves. Using a hexapeptide phage display library, we identified three hexapeptides that react specifically with the anti-beta2GPI mAbs ILA-1, ILA-3, and H-3, which cause endothelial cell activation and induce experimental APS. To enhance the binding of the peptides to the corresponding mAbs, the peptides were lengthened to correspond with the site of the beta2GPI epitope being recognized by these mAbs. As a result, the following three peptides were prepared: A, NTLKTPRVGGC, which binds to ILA-1 mAb; B, KDKATFGCHDGC, which binds to ILA-3 mAb; and C, CATLRVYKGG, which binds to H-3 mAb. Peptides A, B, and C specifically inhibit both in vitro and in vivo the biological functions of the corresponding anti-beta2GPI mAbs. Exposure of endothelial cells to anti-beta2GPI mAbs and their corresponding peptides led to the inhibition of endothelial cell activation, as shown by decreased expression of adhesion molecules (E-selectin, ICAM-1, VCAM-1) and monocyte adhesion. In vivo infusion of each of the anti-beta2GPI mAbs into BALB/c mice, followed by administration of the corresponding specific peptides, prevented the peptide-treated mice from developing experimental APS. The use of synthetic peptides that focus on neutralization of pathogenic anti-beta2GPI Abs represents a possible new therapeutic approach to APS.     

Effect of improved diagnosis of renal cell carcinoma on the course of the disease

The impact of the improved diagnosis of renal cell carcinoma (RCC) on the course of the disease was evaluated in 188 patients who were diagnosed and treated at a single medical center. Sixty-seven patients (group A) who had undergone nephrectomy between 1979 and 1983 for RCC initially diagnosed by intravenous pyelography (IVP) were compared with 121 patients (group B) who had undergone nephrectomy between 1983 and 1989, diagnosed by ultrasound and/or computed tomography (CT) scan. Incidental asymptomatic tumors were found in 18 of 67 (26.9%) group A patients and in 57 of 121 (47.1%) group B patients (P < 0.001). The incidence of small tumors of <5 cm in diameter was significantly lower in group A compared to group B (25.4% vs. 47.9%, respectively, P < 0.01). The disease-free 5-year survival rate for group A was 40% compared to 80% for group B. It is concluded that the introduction of modern imaging techniques has improved the survival of patients with RCC and decreased the progression rate of the disease. © 1994 Wiley-Liss, inc.     

Single-vessel coronary artery stenosis: myocardial perfusion imaging with Gadomer-17 first-pass MR imaging in a swine model of comparison with gadopentetate dimeglumine

PURPOSE: To evaluate the ability of Gadomer-17 to depict perfusion defects in a closed-chest swine model of single-vessel coronary artery disease. MATERIALS AND METHODS: Twelve pigs underwent closed-chest placement of a flow reducer for 70%-90% luminal stenosis in the proximal left anterior coronary artery. Magnetic resonance (MR) perfusion imaging with Gadomer-17 and gadopentetate dimeglumine, microsphere blood flow (MBF) testing, and technetium 99m ((99m)Tc) 2 methoxyisobutylisonitrile (MIBI) single photon emission computed tomography (SPECT) were performed during dipyridamole vasodilation. Comparisons of percentage signal intensity (SI) increase (PSIC) in remote and ischemic myocardium were made with repeated measurements analysis of variance after injection of both tracers. RESULTS: Perfusion defects and reduced PSIC in the anterior ischemic versus the inferior remote myocardium could be identified after injection of both Gadomer-17 (PSIC, 66% +/- 30 [mean +/- SD] vs 100% +/- 32, respectively; P <.001) and gadopentetate dimeglumine (PSIC, 49% +/- 31 vs 81% +/- 43, respectively; P <.005). The size of perfusion defect depicted with both tracers was highly correlated with defect size at (99m)Tc MIBI SPECT (r = 0.69, P <.05 for Gadomer-17 and r = 0.60, P =.05 for gadopentetate dimeglumine) and with areas of reduced MBF (r = 0.70, P <.05 for Gadomer-17 and r = 0.80, P <.05 for gadopentetate dimeglumine). PSIC also correlated with MBF (r = 0.89, P <.001 for Gadomer-17 and r = 0.75, P <.001 for gadopentetate dimeglumine). Gadomer-17 allowed differentiation of ischemic from nonischemic myocardium, as demonstrated by reduced PSIC (PSIC, 48% +/- 38 vs 72% +/- 31, respectively; P <.001) until 20 minutes after contrast material injection. In contrast, differentiation of ischemic from nonischemic myocardium was possible only until 55 seconds after injection of gadopentetate dimeglumine (PSIC, 36% +/- 24 vs 56% +/- 27, respectively; P <.005) but not at any time point thereafter. CONCLUSION: With the study conditions, Gadomer-17 provided more prolonged differentiation of ischemic from remote myocardium than that with gadopentetate dimeglumine.