Effect of Electrode Orientation on Lesion Sizes Produced by Irrigated Radiofrequency Ablation Catheters

Background: Irrigated radiofrequency (RF) ablation catheters may produce different lesion sizes dependent upon the electrode orientation to the tissue. This study examined the effect of irrigated electrode orientation on the lesion size and explores a potential mechanism for this effect.
Methods and Results: Lesions were created in isolated porcine myocardium using an open irrigation, closed irrigation, and nonirrigated RF catheter (all 3.5–4 mm tips). Lesions were created with the electrodes with all permutations of electrode orientation (vertical or horizontal), contact pressure (6 or 20 g), and saline superfusate flow (0.2 or 0.4 m/sec) over tissue interface. The effect of electrode irrigation without RF delivery on tissue temperature was assessed with intramyocardial temperature probes and infrared thermal imaging. For both irrigated catheters, the horizontal orientation produced 25–30% smaller lesion volumes than the vertical orientation despite equal or greater power deliveries. The horizontal orientation produced larger lesion volumes for the nonirrigated catheter. Higher superfusate flow rates were associated with decreased lesion volumes for the irrigated catheters but greater lesion volumes for the nonirrigated catheter. Catheter irrigation alone without RF delivery reduced intramyocardial temperatures up to 4.9°C and the horizontal orientation produced a 2-fold greater area of tissue cooling than the vertical orientation.
Conclusion: Horizontal electrode orientations reduce lesion volumes for irrigated RF catheters. This effect may be in part due to greater areas of active tissue cooling in the horizontal orientation.     

Evidence that human ceruloplasmin molecule consists of homologous parts

The products of spontaneous and induced proteolysis of human ceruloplasmin (Cp) were studied. Some physico-chemical properties of the six fragments with electrophoretically determined Mr 13 0000 (F₁), 110000 (F₂), 66 000 (F₃), 48 000 (F₄) 22 000 (F₅) and 18 000 (F₆) were compared. The amino acid compositions and N-terminal amino acid sequences coincide in F₁–F₅, but differ from those of F₆. Limited tryptic proteolysis of Cp causes the accumulation of polypeptide fragment with Mr 22 000, the N-terminal primary structure of which is identical to that of F₅ produced by spontaneous proteolysis. Electrophoretic fragments of Cp were extracted from polyacrylamide gel, treated with ¹²⁵I and then studied by peptide mapping with subsequent radioautography. The comparison of the “finger prints” showed the identity of F₁ to F₂ and F₃ and gross similarity between F₄ and F₁– F₃. It also revealed similar peptides in F₅ and F₆ hydrolyzates and almost perfect matching of the F₄ map to the map of F₅+ F₆ mixture. On the basis of the obtained data general principles of Cp molecular organization are discussed and intramolecular homology is suggested to be a feature of the protein.     

NMR analysis of a potent decapeptide agonist of human C5a anaphylatoxin

A NMR investigation in H₂0, TFE and DMSO of a conformationally constrained, potent decapeptide agonist of human C5a, YSFKDMPLaR (C5a₆₅-₇₄, Y65, F67, P71, d -Ala73) showed that its N-terminal region (YSFKD) exhibited an extended backbone conformation in H₂O and a more twisted conformation in both TFE/H₂O (30:70, v/v; referred to as TFE) and DMSO. The C-terminal region (MPLaR) of the peptide adopted compact, turn-like structures. In H₂O, the C-terminal region adopted a type II β-turn or a distorted type V/II β-turn involving residues PLaR. In the distorted type V/II β-turn, Leu72 exhibited a conformation typical of a type V β-turn, whereas D -Ala73 exhibited a conformation typical of a type II β-turn. The distorted type V/II β-turn overlapped with an inverse γ-turn involving residues MPL. In DMSO, the C-terminal region had the analogous inverse y-turn and the V/II γ-turn found in H₂O. In many of the DMSO structures, two inverse γ-turns in the MPL and PLa positions formed a double-inverse γ-turn. None of the turns observed in H₂O were present in TFE. However, in TFE, the PLa residues formed an inverse γ-turn. Overall, the turn-like structural motifs in the C-terminal region of the peptide in both H₂O and DMSO (but not in TFE) agreed with the biologically important conformations obtained earlier by the structure-function analysis of a panel of C5a agonist peptides. These motifs may represent key structural elements important for C5a agonist activity and may be used to design the next generation of C5a agonist and antagonist analogues. © Munksgaard 1998.     

EFFECT OF ACUTE AND CHRONIC ETHANOL EXPOSURE ON THE RAT BRAIN OPIATE RECEPTOR FUNCTION

A reduction of the number and a decrease in the dissociationconstant of low-affinity opiate receptor binding sites for metenkephalinin brain membranes was noted in rats after chronic ethanol treatment.These changes were reversed with time, and at 48 hr after withdrawal,tissue from ethanol and pair-fed groups demonstrated similarbinding characteristics. Preincubation of the control rat brainmembrane fraction with the ultrafiltrate of the supernatantobtained from the brain membrane fraction of rats chronicallytreated with ethanol resulted in changes of affinity and numberof opiate receptor binding sites which resembled the changesobserved in rats after long-term treatment with ethanol. Acuteethanol administration (4 g/kg) was shown to eliminate the biphasiccharacter of Scatchard plots usually seen in control animals.Addition of ethanol to control brain membranes was also foundto after significantly the binding of ‘opiate’ peptidesto such membrane fractions.