Differential effects of tetracaine on delayed potassium channels and displacement currents in frog skeletal muscle.

1. Delayed K+-currents and displacement currents were studied with a voltage-clamp technique. 2. In normal fibres, the conductance of the delayed channel grows e-fold per 3 millivolts at sufficiently negative potentials and reaches a limiting value of 2-10 m-mho/cm2 (mean 5-8 m-mho/cm2) at positive potentials. Adding tetracaine (2 mM) reduces the limiting conductance, shifts the voltage-dependence of the delayed channel to +25 mV more positive potentials and slows the kinetics fourfold. 3. By contrast, the displacement currents are virtually unaltered by 2 mM tetracaine. Their voltage-dependence is shifted by less than 5 mV and their kinetics are unaffected. 4. Tetraethylammonium ions (TEA) are known to slow the kinetics of delayed K+-channels fivefold but fail, like tetracaine, to change the kinetics of the displacement currents. 5. Both tetracaine and TEA have thus large effects on the 'gating' of the delayed channel, yet little or none on the displacement currents. This suggests that the displacement currents in skeletal muscle are for the most part unrelated to the opening and closing of delayed channels. It is estimated that 'gating' the delayed channel in muscle may require no more than 1 or 2% of the observed charge displacement.     

Modified syringe design prevents plunger-related contamination--results of contamination and flow-rate tests

The usual mechanism for syringe contamination is spread of micro-organisms along the inside of the barrel. Two or more full strokes of the plunger will inevitably transport a contaminant from the inside wall into the sterile compartment. We modified syringes by replacing the plunger with a modified version that has an additional central O-ring seal. Conventional and modified syringes were tested for their susceptibility to contamination using standard microbiological and radioisotope methods, and the flow-rate stability of the modified syringe design was assessed in a model with commercially available infusion pumps. Although conventional syringes consistently became contaminated with the second full excursion of the plunger, no contamination was observed in modified syringes, even after 100 aspiration/injection cycles. With respect to flow-rate stability, the new syringe design complies with DIN (German Institute for Standardization) standards.     

The decline of potassium permeability during extreme hyperpolarization in frog skeletal muscle

1. The voltage-clamp technique was used to separate the effects of K depletion in the T-system from the decline in K permeability during hyperpolarization, and to characterize the time- and voltage-dependence of the latter.2. K permeability due to the inward rectifier can be described as being proportional to a parameter which diminishes when the membrane is hyperpolarized beyond -120 mV. The parameter obeys first-order kinetics. At 24 degrees C, it can change with a time constant of 49 msec at -150 mV and 25 msec at -65 mV. At -200 mV the fall in membrane conductance due to the permeability change is to 30% of its initial value. The Q(10) for the rate of conductance change at that potential is about 2.8.3. It is estimated that K inward current can lower the average K concentration in the T-system by more than 50%, and that, on the average, the space enclosed by the T-system should be less than 0.8% of the fibre volume. Assuming the T-system space to be 0.3% of the fibre volume, it is calculated that on the average, and during hyperpolarization to about -150 mV, no more than 20% of the initial current should flow across the surface membrane.     

Charge movement in the membrane of striated muscle.

1. Non-linear polarization currents apparently due to permanent dipoles or mobile charges in the membrane can be measured by appropriate comparison of the transient currents required to produce small and large steps of membrane potential. Integration of these transient polarization currents estimates the charge transfer associated with the movement of membrane dipoles or charges. 2. Depolarization from -100 to 0 mV requires a charge transfer of 35 nC/muF in addition to the charge transfer predicted by linear extrapolation of the charge required for a small depolarization from -100 mV. Depolarizations of varying size give a charge-voltage relation which is sigmoid saturating beyond o mV and with a midpoint at about -50 mV. The ratnged depolarization reduces or removes charge movement detected by comparing currents for small and large voltage steps from -100 mV (Charge 1). However in depolarized fibres comparison of currents from a small potential step at +40 mV and a large hyperpolarizing potential step from -20 mV reveals large movements of a second charge (Charge 2). Movement of Charge 2 is less steeply dependent on voltage than movement of Charge 2 both in magnitude and in rate. 4. In size and voltage dependence these two kinds of charge movement correspond to measured voltage dependence of capacity in normally polarized and depolarized fibres (Adrian & Almers, 1976).     

Survival after heart and coronary-artery penetration by an air-rifle projectile

Gunshot injuries of the heart are extremely rare thoracic traumas in Europe during peacetime. Concomitant lesions of the coronary arteries occur in less than 5%. This case reports on a 26-year-old man who was shot with an air rifle at short range. On admission the patient showed signs of pericardial tamponade. Emergency thoracotomy was performed and a frontal cardiac lesion was found in the distal third of the anterior descending branch of the left coronary artery. The bullet crossed the cavum of the left ventricle and remained in the posterior wall in the subepicardial layer adjacent to the posterior descending coronary branch. Under the conditions of extracorporeal circulation we removed the bullet, repaired both ventricle walls using patches in sandwich technique, and bypassed the coronary lesion by single aortocoronary venous graft. No signs of myocardial infarction could be detected by ECG. The follow-up after 3 years shows no cardiac problems and normal stress tolerance. This case report proves that even air rifle shots, which in general are considered to be harmless, may result in life-threatening injuries. For the severity of the injury are decisive the kinetic energy at the muzzle as well as configuration and type of the bullet.     

Adhesion, cytoskeletal architecture and activation status of primary human macrophages on a diamond-like carbon coated surface.

Diamond-like carbon is a promising surface coating for biomedicinal implants like coronary stents or hip joints. Before widespread clinical use of this material, its biocompatibility has to be thoroughly assessed. Cells likely to encounter a diamond-like coated implant in the human body are cells of the monocytic lineage. Their interaction with the diamond-like carbon coated surface will probably critically influence the fate of the implant, as monocytes orchestrate inflammatory reactions and also affect osseointegration of implants. We therefore investigated adhesion, cytoarchitecture and activation status of primary human monocytes and their differentiated derivatives, macrophages, on diamond-like coated glass coverslips using immunofluorescence technique. We show that adhesion of primary monocytes to a diamond-like-coated coverslip is slightly, but not significantly, enhanced in comparison to uncoated coverslips, while the actin and microtubule cytoskeletons of mature macrophages show a normal development. The activation status of macrophages, as judged by polarization of the cell body, was not affected by growth on a diamond-like carbon surface. We conclude that diamond-like carbon shows good indications for biocompatibility to blood monocytes in vitro. It is therefore unlikely that contact with a diamond-like carbon coated surface in the human body will elicit inflammatory signals by these cells.     

MR coil design for simultaneous tip tracking and curvature delineation of a catheter.

In active catheter tracking, small RF coils are attached to the catheter for localization. For interactive catheter steering at vessel branchings, it is necessary to visualize not only a single point near the catheter tip but also the entire shape and orientation of the catheter's distal end. Therefore, a 35-mm-long twisted-pair RF coil was added to a 5 French intravascular catheter with a single tip-tracking coil. With the use of small nonmagnetic electronic components at the catheter tip, and a special switching circuitry outside the catheter, the coil assembly could be operated in two different modes. During MRI, the tip-tracking coil was detuned so that the MR signal was received by the visualization coil only. During tracking, detuning was switched off and the MR signal was predominantly received by the more sensitive tracking coil. The catheter was used in combination with a MR pulse sequence with automatic slice positioning so that the current imaging slice was always placed at the position of the catheter tip. Phantom and animal experiments showed that the catheter tip is better visualized with the combined approach than with a tracking coil alone.     

Percutaneous dilatational tracheostomy — early results and long-term outcome of 326 critically ill patients

Objective: To analyze perioperative and postoperative complications and long-term sequelae following percutaneous dilatational tracheostomy (PDT). Design: A prospective clinical study of patients undergoing PDT. Setting: Seven intensive care units at a University hospital Patients: 326 intensive care patients (202 male, 124 female; age: 11–95 years) with indications for tracheostomy. Interventions: Using tracheoscopic guidance, 337 PDTs were performed according to Ciaglias' method. In 106 decannulated patients, tracheal narrowing was assessed by plain tracheal radiography. Results: Two procedure-related deaths were seen (0.6 %). Perioperative and postoperative complications occurred with 9.5 % of the PDTs. One of 106 patients, who were followed-up for at least 6 months, showed a clinically relevant tracheal stenosis. Subclinical tracheal stenosis of at least 10 % of the cross-sectioned area was recognized in 46 of 106 patients (43.4 %). In the univariate analysis, the degree of stenosis was influenced by the age of the patient (p = 0.044), the duration of intubation prior to PDT (p = 0.042) and by the duration of cannulation (p = 0.006). These parameters had no statistical significance in a multiple regression model. Conclusion: When performed by experienced physicians, percutaneous dilatational tracheostomy under fiberoptic guidance is a safe method. The risks of early complications and of clinically relevant tracheal stenoses are low. Subclinical tracheal stenoses are found in about 40 % of patients following PDT. Received: 25 July 1997 Accepted: 7 April 1998     

Three‐dimensional biexponential weighted 23Na imaging of the human brain with higher SNR and shorter acquisition time

A new method is presented for acquiring 3D biexponential weighted sodium images of the in vivo human brain with up to three times higher signal‐to‐noise ratio compared with conventional six‐step phase‐cycling triple‐quantum‐filtered imaging. To excite and detect multiple‐quantum coherences, a three‐pulse preparation is used. During the pulse train, two images are obtained. The first image is acquired with ultrashort echo time (0.3 ms) during preparation between the first two pulses to yield a spin‐density‐weighted image. After the last pulse, a single‐quantum‐filtered image is acquired with an echo time of 11 ms that maximizes the resulting signal. The biexponential weighted image is calculated by subtracting the single‐quantum‐filtered image from the spin‐density‐weighted image. The resulting image mainly shows signal from sodium ions with biexponential quadrupolar relaxation behavior. In isotropic environments, the resulting image mainly contains triple‐quantum‐filtered signal. The four‐step phase cycling yields similar signal‐to‐noise ratio in shorter acquisition time compared with six‐step phase‐cycling biexponential weighted imaging. Magn Reson Med 70:754–765, 2013. © 2012 Wiley Periodicals, Inc.