Medizin - Open Access LMU - Teil 05/22
About
Available on
Community
250 episodes
1. The nature, distribution and function of rectifying channels in rat spinal root myelinated axons has been assessed with selective blocking agents and a variety of intracellular and extracellular recording techniques. 2. The electrotonic responses of roots poisoned with tetrodotoxin (TTX) to constant current pulses had fast (rise time much less than 1 ms) and slow components, which were interpreted in terms of Barrett & Barrett's (1982) revised cable model for myelinated nerve. Depolarization evoked a rapid outward rectification (time constant, tau approximately 0.5 ms), selectively blocked by 4-aminopyridine (4AP, 1 mM), and a slow outward rectification (tau approximately 15 ms), selectively blocked by tetraethylammonium (TEA, 1 mM) or Ba2+ (0.5 mM). Hyperpolarization evoked an even slower inward rectification, selectively blocked by Cs+ (3 mM) but not by Ba2+. 3. From the different effects of the blocking agents on the fast and slow components of electrotonus, it was deduced (a) that the inward rectification is a property of the internodal axon, (b) that the slow outward rectifier is present at the nodes, and probably the internodes as well, and (c) that the 4AP-sensitive channels have a minor nodal and a major internodal representation. 4. TEA and Ba2+ reduced the accommodation of roots and fibres not poisoned with TTX to long current pulses, whereas 4AP facilitated short bursts of impulses in response to a single brief stimulus. 5. TEA and Ba2+ also abolished a late hyperpolarizing after-potential (peaking at 20-80 ms), while 4AP enhanced the depolarizing after-potential in normal fibres, and abolished an early hyperpolarizing after-potential (peaking at 1-3 ms) in depolarized fibres. Corresponding to the later after-potentials were post-spike changes in excitability and conduction velocity, which were affected similarly by the blocking agents. Cs+ increased the post-tetanic depression attributable to electrogenic hyperpolarization. 6. The physiological roles of the three different rectifying conductances are discussed. It is also argued that the prominent ohmic 'leak conductance', usually ascribed to the nodal axon, must arise in an extracellular pathway in series with the rectifying internodal axon.
Double-barrelled ion-sensitive microelectrodes were used to measure changes in the intracellular activities of K+, Na+, and Cl- (aKi, aNai, aCli) in neurones of rat sympathetic ganglia and in glial cells of slices from guinea-pig olfactory cortex. In sympathetic neurones, carbachol and gamma-aminobutyric acid (GABA) produced a reversible decrease of aKi. The decrease of aKi during carbachol was accompanied by a rise of aNai, whereas in the presence of GABA decreases of aKi and aCli were seen. The reuptake of K+ released during the action of carbachol was completely blocked by ouabain, whereas furosemide inhibited the aKi recovery after the action of GABA. In glial cells, in contrast to the observations in the sympathetic neurones, aKi and aCli increased, whereas aNai decreased when neuronal activity was enhanced by repetitive stimulation of the lateral olfactory tract. It was found that barium ions and ouabain strongly reduced the activity-related rise of intraglial aKi in slices of guinea-pig olfactory cortex. These data show that mammalian neurones as well as glial cells possess several K+ uptake mechanisms that contribute to potassium homeostasis. Ouabain, furosemide, and Ba2+ are useful pharmacological tools to separate these mechanisms.
The mechanism leading to hyperlipidemia in the nephrotic syndrome is not fully understood but may be related in part to loss of high density lipoproteins in the urine of patients with nephrosis. To prove this hypothesis, we compared serum lipoprotein profiles with the excretion of high density lipoproteins in urine in 19 nephrotic patients. Serum cholesterol ranged from 19–152 (median value 45) mg/dl in very low density lipoproteins (VLDL), from 130–443 (median 186) mg/dl in low density lipoproteins (LDL) and from 19–64 (median 33) mg/dl in high density lipoproteins (HDL). Hyperlipoproteinemia was found in 17 patients, which was classified as phenotype IIa (Fredrickson) in 2, as phenotype IIb in 9 and as phenotype IV in 6 subjects. Two patients showed normal lipoprotein patterns. VLDL- and LDL-cholesterol were not found in detectable amounts in urine, whereas HDL-cholesterol was measured in low concentrations from 0.1–8.3 mg/24 h in all samples. There was no correlation between serum HDL-cholesterol and urinary HDL-cholesterol, but a positive correlation between serum LDL-cholesterol and urinary HDL-cholesterol (r= +0.54, p < 0.05). However, the total amount of the daily urinary loss of HDL (
A case where the severe course of an orbital phlegmon led to a functionally and cosmetically poor condition is presented. Thirty-five years later, it was possible to achieve a satisfactory result through several operations performed with interdisciplinary cooperation. The orbit and forehead were reconstructed with porous polyethylene, thus ensuring a cosmetically good result. In two operations, the left eye was freed from its upward fixation through cicatrectomy and mobilization of the mucles, so that the eyes were straight again in the primary position. There is a limited binocular visual field. Binocular vision could be restored again after an interruption of 35 years.
The findings of Hill et al. (1984) on the greatly enhanced transformation frequencies at very low dose rates of fission neutrons induced us to perform an analogous study with -particles at comparable dose rates. Transformation frequencies were determined with γ-rays at high dose rate (0·5 Gy/min), and with -particles at high (0·2 Gy/min) and at low dose rates (0·83-2·5 mGy/min) in the C3H 10T1/2 cell system. α-particles were substantially more effective than γ-rays, both for cell inactivation and for neoplastic transformation at high and low dose rates. The relative biological effectiveness (RBE) for cell inactivation and for neoplastic transformation was of similar magnitude, and ranged from about 3 at an -particle dose of 2 Gy to values of the order of 10 at 0·25 Gy. In contrast to the experiments of Hill et al. (1984) with fission neutrons, no increased transformation frequencies were observed when the -particle dose was protracted over several hours.
The discovery of the first well-defined natriuretic hormone, the Atrial Natriuretic Factor (ANF), has prompted research on its impact on volume regulation in health and disease. The natriuretic, diuretic, and smooth muscle-relaxing properties suggest an important role of this novel hormone in pathophysiological states with sodium or volume retention, such as congestive heart failure or cirrhosis of the liver. Investigations on the implications of ANF in liver disease have been performed for little more than 1 year, and results are still controversial in many respects. At present, it seems very likely that there is no absolute deficiency of plasma ANF in patients with cirrhosis. Moreover, elevated plasma levels in cirrhotics with ascites have been reported by several groups. However, as yet, a molecular characterization of this increased immunoreactivity is still lacking. There is disagreement on the reduced release of and renal response to ANF in subgroups of cirrhotics; however, stimulus-response-coupling might be impaired. Further studies are needed to elucidate the pathophysiological implications and therapeutical potential of ANF in patients with chronic liver disease.
1. The characteristics of long-duration inhibitory postsynaptic potentials (l-IPSPs) which are evoked in rat frontal neocortical neurons by local electrical stimulation were investigated with intracellular recordings from anin vitro slice preparation. 2. Stimulation with suprathreshold intensities evoked l-IPSPs with typical durations of 600–900 msec at resting membrane potential. Conductance increases of 15–60% were measured at the peak amplitude of l-IPSPs (150–250 msec poststimulus). 3. The duration of the conductance increases during l-IPSPs displayed a significant voltage dependence, decreasing as the membrance potential was depolarized and increasing with hyperpolarization. 4. The reversal potential of l-IPSPs is significantly altered by reductions in the extracellular potassium concentration. Therefore it is concluded that l-IPSPs in rat neocortical neurons are generated by the activation of a potassium conductance. 5. l-IPSPs exhibit stimulation fatigue. Stimulation with a frequency of 1 Hz produces a complete fatigue of the conductance increases during l-IPSPs after approximately 20 consecutive stimuli. Recovery from this fatigue requires minutes. 6. l-IPSPs are not blocked by bicuculline but are blocked by baclofen.
The murine immediate-early (IE) protein pp89 is a nonstructural virus- encoded phosphoprotein residing in the nucleus of infected cells, where it acts as transcriptional activator. Frequency analysis has shown that in BALB/c mice the majority of virus-specific CTL recognize IE antigens. The present study was performed to assess whether pp89 causes membrane antigen expression detected by IE-specific CTL. Site-directed mutagenesis has been used to delete the introns from gene ieI, encoding pp89, for subsequent integration of the continuous coding sequence into the vaccinia virus genome. After infection with the vaccinia recombinant, the authentic pp89 was expressed in cells that became susceptible to lysis by an IE-specific CTL clone. Priming of mice with the vaccinia recombinant sensitized polyclonal CTL that recognized MCMV- infected cells and transfected cells expressing pp89. Thus, a herpesviral IE polypeptide with essential function in viral transcriptional regulation can also serve as a dominant antigen for the specific CTL response of the host.
1. Double-barrelled ion-sensitive micro-electrodes were used to measure changes in the intracellular activities of K+, Na+ and Cl- (aiK, aiNa, aiCl) in glial cells of slices from guinea-pig olfactory cortex during repetitive stimulation of the lateral olfactory tract. 2. Base-line levels of aiK, aiNa and aiCl were about 66, 25 and 6 mM, respectively, for cells with resting potentials higher than -80 mV. During stimulation, intraglial aiK and aiCl increased, whereas aiNa decreased. Within about 2 min after stimulation the ion activities returned to their base-line levels. 3. The Cl- equilibrium potential was found to be close to the membrane potential (Em). There was also a strong correlation between changes of Em and aiCl. These observations indicate a high Cl- conductance of the glial cell membrane. 4. In the presence of Ba2+, the usual depolarizing response of the glial cells to a rise of the extracellular K+ activity (aeK) reversed into a membrane hyperpolarization. Furthermore, Ba2+ strongly reduced the stimulus-related rise of intraglial aiK. An additional application of ouabain blocked both the membrane hyperpolarization as well as the remaining rise of aiK. 5. In conclusion, our data show that glial cells in guinea-pig olfactory cortex slices possess at least two mechanisms of K+ accumulation. One mechanism is sensitive to the K+ channel blocker Ba2+ and might be a passive KCl influx. The other appears to be the electrogenic Na+/K+ pump, which can be activated by excess extracellular K+.
We have constructed target cells by cotransfection of the MHC gene Ld and fragments of murine cytomegalovirus (MCMV) DNA coding for nonstructural immediate-early (IE) proteins. Transfectants were tested by using CTL clone IE1 with specificity for an IE epitope presented in association with Ld. Data show that clone IE1 recognizes a product of the ie1 transcription unit of MCMV, and that its specificity is shared by approximately 25% of polyclonal IE-specific CTL. The results provide the first definite evidence that expression of a herpes virus IE gene encoding a regulatory protein gives rise to antigen expression detectable by specific CTL
To study the mechanism of periodic paralysis, we investigated the properties of intact muscle fibers biopsied from a patient who had adynamia episodica hereditaria with electromyographic signs of myotonia. When the potassium concentration in the extracellular medium, [K]e, was 3.5 mmol/l, force of contraction, membrane resting potential, and intracellular sodium activity were normal, but depolarizing voltage clamp steps revealed the existence of an abnormal inward current. This current was activated at membrane potentials less negative than -80 mV, reached a maximum within 50 msec, and was not inactivated with time. The inward current was completely and reversibly blocked by tetrodotoxin, which indicates that it was carried by sodium ions. In a solution containing 9 mmol/l potassium, normal muscle would depolarize to -63 mV and yet be capable of developing full tetanic force upon stimulation. The muscle from the patient depolarized to -57 mV and became inexcitable, i.e., it was paralyzed. A contracture did not develop. Lowering of the extracellular pH did not influence the resting potential, but it effectively antagonized or prevented the paralytic effect of high [K]e by changing the inactivation characteristics of the sodium channels. Hydrochlorothiazide, which had a therapeutic effect on the patient, did not prevent paralysis in vitro. An abnormal rise of the intracellular sodium activity was recorded when the extracellular potassium concentration was raised to 10 mmol/l.
1. Intracellular recordings were obtained from neurones in layers 2 and 3 of the rat frontal neocortex in an in vitro slice preparation. Three distinct types of stimulation-evoked post-synaptic potentials were recorded in these neurones: excitatory post-synaptic potentials (e.p.s.p.s); bicuculline-sensitive, chloride-dependent inhibitory post-synaptic potentials (i.p.s.p.s) with times to peak of 20-25 ms (fast(f)-i.p.s.p.s); bicuculline-insensitive, potassium-dependent i.p.s.p.s with bicuculline-insensitive, potassium-dependent i.p.s.p.s with times to peak of 150-250 ms (long(l)-i.p.s.p.s). 2. The effects of baclofen were investigated on seventy-one neurones. Baclofen was applied by ionophoresis or pressure ejection from micropipettes or was added to the superfusion medium. 3. Baclofen depressed stimulation-evoked e.p.s.p.s in fifty-seven of the sixty neurones tested. This effect was associated with an increase in the stimulation intensity required to produce a synaptically evoked action potential for thirty-nine of forty-four neurones. 4. Baclofen depressed f-i.p.s.p.s in thirty-seven of the thirty-nine neurones tested and l-i.p.s.p.s in each one of the seventeen neurones tested. Reversal potential values for each type of i.p.s.p. were not changed by baclofen and its depressions of each were independent of membrane potential (Em). Baclofen reduced the magnitude and the duration of the conductance increases that were associated with f- and l-i.p.s.p.s. 5. Baclofen hyperpolarized forty of seventy-one neurones and produced outward currents in three of four neurones recorded in voltage clamp at holding potentials between -55 and -65 mV. These actions were associated with 10-58% reductions of neuronal input resistance (RN) and 10-20% increases in neuronal input conductance (gN), respectively. Baclofen decreased the direct excitability of twenty-three of twenty-seven neurones tested. Determinations of the reversal potential for baclofen-induced changes of Em indicate that baclofen increases the conductance of rat neocortical neurones to potassium ions. 6. The EC50 for each action of DL-baclofen was approximately 1 microM. L-Baclofen was greater than 100 times more potent than D-baclofen. 7. Concentrations of bicuculline that blocked f-i.p.s.p.s and responses to ionophoretically applied gamma-aminobutyric acid (GABA) had no effect on the depressions of e.p.s.p.s or the hyperpolarizations and decreases in RN that baclofen produced. 8. Baclofen did not reduce the duration of action potentials that were prolonged with intracellular injections of caesium ions or by superfusions with medium that contained 10 mM-tetraethylammonium (TEA).
Intracellular recordings were obtained from rat neocortical neurons in vitro. The current-voltage-relationship of the neuronal membrane was investigated using current- and single-electrode-voltage-clamp techniques. Within the potential range up to 25 mV positive to the resting membrane potential (RMP: –75 to –80 mV) the steady state slope resistance increased with depolarization (i.e. steady state inward rectification in depolarizing direction). Replacement of extracellular NaCl with an equimolar amount of choline chloride resulted in the conversion of the steady state inward rectification to an outward rectification, suggesting the presence of a voltage-dependent, persistent sodium current which generated the steady state inward rectification of these neurons. Intracellularly injected outward current pulses with just subthreshold intensities elicited a transient depolarizing potential which invariably triggered the first action potential upon an increase in current strength. Single-electrode-voltage-clamp measurements reveled that this depolarizing potential was produced by a transient calcium current activated at membrane potentials 15–20 mV positive to the RMP and that this current was responsible for the time-dependent increase in the magnitude of the inward rectification in depolarizing direction in rat neocortical neurons. It may be that, together with the persistent sodium current, this calcium current regulates the excitability of these neurons via the adjustment of the action potential threshold.
We have shown in a murine model system for cytomegalovirus (CMV) disease in the immunocompromised host that in vivo application of recombinant human IL-2 (rhIL-2) can enhance the antiviral effect of a limited number of CD8+T lymphocytes, not only in prophylaxis, but also in therapy, when virus has already colonized host tissues. The observed net effect of IL-2 was consistent with the assumption of daily effector population doublings. The prospects for IL-2-supported immunotherapy of established CMV infection depend upon the tissues involved in disease. It appears that the prospects for controlling established CMV adrenalitis are less promising than for a therapy of interstitial CMV pneumonia.
The responses of rat neocortical neurons in vitro to iontophoretically applied N-methyl-d-aspartate (NMDA) were investigated by means of intracellular recording in the presence and absence of extracellular magnesium ions (Mg2+). At Mg2+-concentrations of 1.3 mM the neurons responded with a depolarization accompanied by an increase in membrane resistance. Upon removal of Mg2+ the NMDA-induced depolarization was markedly potentiated. However, even in neurons recorded from slices which were incubated in a Mg2+-free solution for 3–7 h, the NMDA response was still associated with a resistance increase, suggesting that the voltage-dependence of the NMDA-activated conductance is not exclusively determined by Mg2+.
