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A Olschewski

Publications and source records attributed to A Olschewski.

13 recordsLinked to original sources
PubMed2005

[Ecarin chromogenic assay: an innovative test for quantitative determination of direct thrombin inhibitors in plasma].

The ecarin chromogenic assay (ECA) was developed for quantitative determination of direct thrombin inhibitors. As a further development of the ecarin clotting time (ECT), the ECA is based on the same principle, the activation of prothrombin by ecarin a snake venom from Echis carinatus. In the ECA the prothrombin activation products meizothrombin and meizothrombin-desF1 cleave a chromogenic substrate, whereas in the clotting assay ECT plasma fibrinogen is converted to fibrin. The activity of meizothrombin/meizothrombin-desF1 is inhibited in a concentration-dependent fashion by direct thrombin inhibitors. The ECA can be used as ECA-H for quantitative determination of hirudin and as ECA-T for determination of synthetic thrombin inhibitors. As shown for hirudin, argatroban and melagatran, the ECA turned out as a very precise and sensitive method, which combines the advantages of ECT with those of chromogenic assays. In ECA very low interindividual variations were found compared to aPTT and even ECT. The ECA is independent of the variations of the coagulation variables prothrombin and fibrinogen.

Animals↗
PubMed2005

Effect of normoxia and hypoxia on K(+) current and resting membrane potential of fetal rabbit pulmonary artery smooth muscle.

At birth, the increase in O(2) tension (pO(2)) is an important cause of the decrease in pulmonary vascular resistance. In adult animals there are impressive interspecies differences in the level of hypoxia required to elicit a pulmonary vasoconstrictor response and in the amplitude of the response. Hypoxic inhibition of some potassium (K(+)) channels in the membrane of pulmonary arterial smooth muscle cells (PASMCs) helps to initiate hypoxic pulmonary vasoconstriction. To determine the effect of the change in pO(2) on fetal rabbit PASMCs and to investigate possible species-dependent differences, we measured the current-voltage relationship and the resting membrane potential, in PASMCs from fetal resistance arteries using the amphotericin-perforated patch-clamp technique under hypoxic and normoxic conditions. Under hypoxic conditions, the K(+) current in PASMCs was small, and could be inhibited by 4-aminopyridine, iberiotoxin and glibenclamide, reflecting contributions by Kv, K(Ca) and K(ATP) channels. The average resting membrane potential was -44.3+/-1.3 mV (n=29) and could be depolarized by 4-AP (5 mM) and ITX (100 nM) but not by glibenclamide (10 microM). Changing from hypoxia, that mimicked fetal life, to normoxia dramatically increased the K(Ca) and consequently hyperpolarized (-9.3+/-1.7 mV; n=8) fetal rabbit PASMCs. Under normoxic conditions K(+) current was reduced by 4-AP with a significant change in resting membrane potential (11.1+/-1.7 mV; n=8). We conclude that resting membrane potential in fetal rabbit PASMCs under both hypoxic and normoxic conditions depends on both Kv and K(Ca) channels, in contrast to fetal lamb or porcine PASMCs. Potential species differences in the K(+) channels that control resting membrane potential must be taken into consideration in the interpretation of studies of neonatal pulmonary vascular reactivity to changes in O(2) tension.

Animals↗
PubMed2001

Effect of drugs used for neuropathic pain management on tetrodotoxin-resistant Na(+) currents in rat sensory neurons.

BACKGROUND: Tetrodotoxin-resistant Na(+) channels play an important role in generation and conduction of nociceptive discharges in peripheral endings of small-diameter axons of the peripheral nervous system. Pathophysiologically, these channels may produce ectopic discharges in damaged nociceptive fibers, leading to neuropathic pain syndromes. Systemically applied Na(+) channel--blocking drugs can alleviate pain, the mechanism of which is rather unresolved. The authors investigated the effects of some commonly used drugs, i.e., lidocaine, mexiletine, carbamazepine, amitriptyline, memantine, and gabapentin, on tetrodotoxin-resistant Na+ channels in rat dorsal root ganglia. METHODS: Tetrodotoxin-resistant Na(+) currents were recorded in the whole-cell configuration of the patch-clamp method in enzymatically dissociated dorsal root ganglion neurons of adult rats. Half-maximal blocking concentrations were derived from concentration-inhibition curves at different holding potentials (-90, -70, and -60 mV). RESULTS: Lidocaine, mexiletine, and amitriptyline reversibly blocked tetrodotoxin-resistant Na(+) currents in a concentration- and use-dependent manner. Block by carbamazepine and memantine was not use-dependent at 2 Hz. Gabapentin had no effect at concentrations of up to 3 mm. Depolarizing the membrane potential from -90 mV to -60 mV reduced the available Na(+) current only by 23% but increased the sensitivity of the channels to the use-dependent blockers approximately fivefold. The availability curve of the current was shifted by 5.3 mV to the left in 300 microm lidocaine. CONCLUSIONS: Less negative membrane potential and repetitive firing have little effect on tetrodotoxin-resistant Na(+) current amplitude but increase their sensitivity to lidocaine, mexiletine, and amitriptyline so that concentrations after intravenous administration of these drugs can impair channel function. This may explain alleviation from pain by reducing firing frequency in ectopic sites without depressing central nervous or cardiac excitability.

Amitriptyline↗
PubMed2001

Suppression of potassium conductance by droperidol has influence on excitability of spinal sensory neurons.

BACKGROUND: During spinal and epidural anesthesia with opioids, droperidol is added to prevent nausea and vomiting. The mechanisms of its action on spinal sensory neurons are not well understood. It was previously shown that droperidol selectively blocks a fast component of the Na+ current. The authors studied the action of droperidol on voltage-gated K+ channels and its effect on membrane excitability in spinal dorsal horn neurons of the rat. METHODS: Using a combination of the patch-clamp technique and the "entire soma isolation" method, the action of droperidol on fast-inactivating A-type and delayed-rectifier K+ channels was investigated. Current-clamp recordings from intact sensory neurons in spinal cord slices were performed to study the functional meaning of K+ channel block for neuronal excitability. RESULTS: Droperidol blocked delayed-rectifier K+ currents in isolated somata of dorsal horn neurons with a half-maximum inhibiting concentration of 20.6 microm. The A-type K+ current was insensitive to up to 100 microm droperidol. At droperidol concentrations insufficient for suppression of an action potential, the block of delayed-rectifier K+ channels led to an increase in action potential duration and, as a consequence, to lowering of the discharge frequency in the neuron. CONCLUSIONS: Droperidol blocks delayed-rectifier K+ channels in a concentration range close to that for suppression of Na+ channels. The block of delayed-rectifier K+ channels by droperidol enhances the suppression of activity in spinal sensory neurons at drug concentrations insufficient for complete conduction block.

Animals↗
PubMed2001

Basic electrical properties of in situ endothelial cells of small pulmonary arteries during postnatal development.

Small pulmonary arteries are the major determinants of pulmonary artery pressure and vascular resistance. Their endothelium modulates pulmonary resistance, remodeling, and blood fluidity. We developed a method that provides access to the luminal surface of small pulmonary arteries of rat and allows the patch-clamp study of electrical properties of in situ endothelium. At birth, the membrane was predominantly permeable for K(+), showing a resting potential of -70 mV. This conductance was not voltage-dependent and was insensitive to standard blockers of K(+) channels such as tetraethylammonium, charybdotoxin, and 4-aminopyridine. The first 22 d of development were accompanied by an additional expression of a Cl(-) conductance, increasing membrane potential to -45 mV. Acidosis reduced K(+) conductance and depolarized the membrane, whereas alkalosis resulted in hyperpolarization. Two-electrode recordings revealed tight electrical coupling (83%) between neighboring cells in the circumferential direction of the artery. The electrotonic length constant for endothelium was 13.3 microm, indicating that most cells in one cross section of a small artery are well coupled. Thus, the resting membrane conductances in small pulmonary artery endothelial cells change with postnatal development and are modulated by pH.

Age Factors↗
PubMed2000

Block of neuronal tetrodotoxin-resistant Na+ currents by stereoisomers of piperidine local anesthetics.

Tetrodotoxin (TTX)-sensitive Na(+) channels in the peripheral nervous system are the major targets for local anesthetics. In the peripheral nociceptive system, a Na(+) channel subtype resistant to TTX and with distinct electrophysiological properties seems to be of importance for impulse generation and conduction. A current through TTX-resistant Na(+) channels displays slower activation and inactivation kinetics and has an increased activation threshold compared with TTX-sensitive Na(+) currents and may have different pharmacological properties. We studied the effects of stereoisomers of piperidine local anesthetics on neuronal TTX-resistant Na(+) currents recorded with the whole-cell configuration of the patch clamp method in enzymatically dissociated dorsal root ganglion neurons of adult rats. Stereoisomers of mepivacaine, ropivacaine, and bupivacaine reversibly inhibited TTX-resistant Na(+) currents in a concentration and use-dependent manner. All drugs accelerated time course of inactivation. Half-maximal blocking concentrations were determined from concentration-inhibition relationships. Potencies for tonic and for use-dependent block increased with rising lipid solubilities of the drugs. Stereoselective action was not observed. We conclude that block of TTX-resistant Na(+) currents may lead to blockade of TTX-resistant action potentials in nociceptive fibers and consequently may be responsible for pain suppression during local anesthesia.

Algorithms↗
PubMed2000

Differential block of fast and slow inactivating tetrodotoxin-sensitive sodium channels by droperidol in spinal dorsal horn neurons.

BACKGROUND: Dorsal horn neurons of the spinal cord participate in neuronal pain transmission. During spinal and epidural anesthesia, dorsal horn neurons are exposed to local anesthetics and opioids. Droperidol is usually given with opioids to avoid nausea and vomiting. A recently developed method of "entire soma isolation" has made it possible to study directly the action of droperidol on different components of Na+ current in dorsal horn neurons. METHODS: Using a combination of the whole-cell patch-clamp recording from spinal cord slices and the entire soma isolation method, we studied the direct action of droperidol on two types of Na+ currents in dorsal horn neurons of young rats. RESULTS: The tetrodotoxin-sensitive Na+ current in isolated somata consisted of a fast inactivating (tauF, 0.5-2 ms; 80-90% of the total amplitude) and a slow inactivating (tauS, 6-20 ms; 10-20% of the total amplitude) component. Droperidol, at concentrations relevant for spinal and epidural anesthesia, selectively and reversibly suppressed the fast component with a half-maximum inhibiting concentration (IC50) of 8.3 microm. The slow inactivating component was much less sensitive to droperidol; the estimated IC50 value was 809 microm. CONCLUSIONS: Droperidol selectively blocks fast Na+ channels, the fast and slow components of the Na+ current in dorsal horn neurons are carried through pharmacologically distinct types of Na+ channels, and the effects of droperidol differ from those of local anesthetics and tetrodotoxin, which equipotently suppress both components. Droperidol may be suggested as a pharmacologic tool for separation of different types of inactivating tetrodotoxin-sensitive Na+ channel.

Adjuvants, Anesthesia↗
PubMed1999

Effect of bupivacaine on ATP-dependent potassium channels in rat cardiomyocytes.

Bupivacaine induces fatal arrhythmia when accidentally injected i.v. or overdosed, whereas lidocaine is used as an anti-arrhythmic agent. We have suggested recently that the anti-arrhythmic effect of lidocaine may be explained by suppression of ATP-sensitive potassium (KATP) channels. Therefore, it could be argued that different sensitivities of KATP channels to both drugs could be a reason for their different arrhythmic and anti-arrhythmic properties. In this study, we have investigated the direct action of bupivacaine on KATP channels in cardiomyocytes. The effects of bupivacaine on the cardiac KATP channel were investigated using the patch-clamp technique on enzymatically dissociated cardiomyocytes of adult rats. Bupivacaine was applied to the outer side of excised membrane patches using a multiple-barrel perfusion system. Concentration-response curves indicated that bupivacaine blocked the mean current of the KATP channels at a half-maximum inhibiting concentration (IC50) of 29 mumol litre-1, similar to that reported for lidocaine (43 mumol litre-1). Binding of bupivacaine influenced the gating of this channel, but did not reduce the conductance of the open channel. Bupivacaine and lidocaine were equipotent in blocking KATP channels. However, because of its excessive block of the sodium channel in the inactivated state, block of KATP channels by bupivacaine will only enhance its cardiotoxicity.

Adenosine Triphosphate↗
PubMed1998

Blockade of Na+ and K+ currents by local anesthetics in the dorsal horn neurons of the spinal cord.

BACKGROUND: The dorsal horn of the spinal cord is a pivotal point for transmission of neuronal pain. During spinal and epidural anesthesia, the neurons of the dorsal horn are exposed to local anesthetics. Unfortunately, little is known about the action of local anesthetics on the major ionic conductances in dorsal horn neurons. In this article, the authors describe the effects of bupivacaine, lidocaine, and mepivacaine on voltage-gated Na+ and K+ currents in the membranes of these neurons. METHODS: The patch-clamp technique was applied to intact dorsal horn neurons from laminae I-III identified in 200-microm slices of spinal cord from newborn rats. Under voltage-clamp conditions, the whole-cell Na+ and K+ currents activated by depolarization were recorded in the presence of different concentrations of local anesthetics. RESULTS: Externally applied bupivacaine, lidocaine, and mepivacaine produced tonic block of Na+ currents with different potencies. Half-maximum inhibiting concentrations (IC50) were 26, 112, and 324 microM, respectively. All local anesthetics investigated also showed a phasic, that is, a use-dependent, block of Na+ channels. Rapidly inactivating K+ currents (KA currents) also were sensitive to the blockers with IC50 values for tonic blocks of 109, 163, and 236 microM, respectively. The block of KA currents was not use dependent. In contrast to Na+ and KA currents, delayed-rectifier K+ currents were almost insensitive to the local anesthetics applied. CONCLUSIONS: In clinically relevant concentrations, local anesthetics block Na+ and KA currents but not delayed-rectifier K+ currents in spinal dorsal horn neurons. The molecular mechanisms of Na+ and K+ channel block by local anesthetics seem to be different. Characterization of these mechanisms could be an important step in understanding the complexity of local anesthetic action during spinal and epidural anesthesia.

Anesthetics, Local↗
PubMed1996

ATP-dependent potassium channel in rat cardiomyocytes is blocked by lidocaine. Possible impact on the antiarrhythmic action of lidocaine.

BACKGROUND: During myocardial ischemia, lidocaine has favorable antiarrhythmic properties. Malignant arrhythmias result from heterogeneity between ischemic and nonischemic regions in extracellular potassium concentration and action potential duration. These effects have been attributed to the activation of ATP-dependent potassium (KATP) channels. In this study, we investigated the action of lidocaine on the KATP channels to test the possible link between the antiarrhythmic properties of lidocaine and its action on the KATP channel. METHODS AND RESULTS: The patch-clamp technique was employed on enzymatic dissociated cardiomyocytes of adult rats. Lidocaine was applied to the outer side of excised membrane patches by means of a multibarrel perfusion system. Lidocaine reversibly blocked the mean current of the KATP channels in a concentration-dependent manner (IC50 = 43 +/- 4.7 mumol/L, E = 0 mV, n = 6), while the amplitude of the single-channel current remained unchanged. The half-maximum blocking concentration corresponds to the therapeutic range for the antiarrhythmic application of a lidocaine bolus in humans. CONCLUSIONS: The open probability but not the conductance of the KATP channel in the membrane of rat cardiomyocytes is blocked by lidocaine. This action may explain, in part, the favorable antiarrhythmic properties of lidocaine during acute myocardial ischemia.

Adenosine Triphosphate↗