Functional aspects of dexamethasone upregulated nicotinic acetylcholine receptors in C2C12 myotubes.

Three days of treatment with the glucocorticoid dexamethasone (1 nM-1 microM) induced a concentration-dependent up-regulation of muscle nicotinic acetylcholine receptor (nAChR) in C2C12 mouse myotubes (EC50 = 10 +/- 7.3 nM), as assessed by [3H]alpha-BuTx binding. The maximum increase in binding amounted 148 +/- 17.6% of control. Parallel electrophysiological measurements employed the patch-clamp technique in cell-attached configuration. The nAChR single channel properties were investigated in the presence of carbachol (1 microM) in the pipette. Treatment with dexamethasone (1 microM, 1-5 days) induced an increase in the number of patches showing channel activity from 30 to 70%. Ion channel characteristics did not differ significantly in control and dexamethasone treated myotubes. Conductance was 32 +/- 3 vs 31 +/- 2 pS, respectively. The time constants of open time events tau 1 and tau 2 were 0.6 +/- 0.1 and 6.6 +/- 1 ms vs 0.6 +/- 0.1 and 6.6 +/- 1 ms, respectively. Closed duration's tau 1 and tau 2 were 1.1 +/- 0.2 and 110 +/- 12 ms vs 1.2 +/- 0.3 and 107 +/- 18 ms. In conclusion, dexamethasone upregulated nAChRs are functional and their electrophysiological parameters are similar to those found in control myotubes.

The general anesthetic propofol inhibits transmembrane calcium current in chick sensory neurons.

The action of propofol on voltage-gated calcium channels was investigated in cultured dorsal root ganglion neurons from chick embryos. The Ca2+ current was measured by using the patch-clamp technique in whole cell configuration. Low-voltage-activated (LVA) and high-voltage-activated (HVA) Ca2+ currents were selected by means of appropriate stimulation protocols. Propofol (0.3 mM) inhibited the LVA T-type current by 80% (P < 0.001). The same concentration of propofol reduced the HVA Ca2+ current with a high variability (10%-75%). The inactivation time constant of the HVA current was also shortened to 50% by propofol. omega-Conotoxin and nifedipine were used to discriminate between the HVA N- and L-type current components. Only the L-type component was strongly depressed (75%) by propofol (P < 0.001); different effects on the HVA current might, therefore, reflect different percentages of L- and N-type channels in neurons. We conclude that propofol inhibits the T-type and L-type components of the Ca2+ current. This inhibition may play a role in the cardiovascular side effects clinically observed.

Clinical concentrations of edrophonium enhance desensitization of the nicotinic acetylcholine receptor.

The principal acetylcholinesterase inhibitors used in clinical practice, edrophonium, neostigmine, and pyridostigmine, differ in their abilities to reverse profound neuromuscular block. This difference may reflect differential inhibition of the nicotinic acetylcholine receptor (nAChR) itself. To investigate this possibility, we studied the effects of these drugs on the function of nAChR (alpha 2 beta gamma delta subtype expressed in Xenopus laevis oocytes) using a whole-cell voltage clamp technique. All three drugs produced concentration-dependent inhibition of nAChR currents induced by the nicotinic agonist dimethylphenyl piperazinium iodide (DMPP). However, only with edrophonium did the effective inhibitory concentration overlap with the clinical range, producing 47% inhibition of nAChR current at the peak serum concentration (60 microM) obtained from a 1 mg/kg dose. The inhibition by edrophonium was voltage-dependent, being more potent at hyperpolarized membrane potentials [IC50(-60 mV) = 82.1 +/- 5.0 microM; IC50(-90 mV) = 50.8 +/- 2.7 microM; IC50(-120 mV) = 41.1 +/- 1.3 microM] and implying some degree of channel block within the ion-conducting pore. Edrophonium also enhanced desensitization of the nAChR within the clinically observed range. Edrophonium desensitization of the nAChR was further increased by simultaneous exposure to other drugs known to promote desensitization of the receptor. These two mechanisms, channel block and enhanced desensitization, may provide molecular explanations for the lesser capacity of edrophonium to promote complete reversal of profound neuromuscular block.

Extracellular pancuronium affects sodium current in chick embryo sensory neurones.

1. The action of pancuronium on transmembrane sodium conductance was investigated in dorsal root ganglion neurones of chick embryos. The Na+ current was measured by use of the patch-clamp technique in whole-cell configuration. 2. Externally perfused pancuronium (50 microM to 1 mM) reversibly inhibited the current by a fast mechanism of action. Inhibition was concentration-dependent (with a half-effective dose of 170 microM) but not voltage-dependent. 3. The activation and inactivation kinetics of the Na+ current were estimated in pancuronium and in control solution by fitting experimental data with a Hodgkin-Huxley theoretical model. 4. The activation time constant tau m, at negative membrane voltages, was larger in the presence of pancuronium than in the control. In contrast, the inactivation time constant tau h was smaller during drug perfusion at membrane voltages < -10 mV. The steady-state inactivation h infinity was not affected by pancuronium. 5. These results suggest that pancuronium may reduce the sodium current by interacting with the sodium channels in both the resting and open states.

K+ channels in PC12 cells are affected by propofol.

The effect on K+ currents (IK) of the general anaesthetic propofol (PR) (2,6-diisopropylphenol) was tested in undifferentiated clonal pheochromocytoma (PC 12) cells using the patch-clamp technique in whole-cell and single-channel configurations. PR decreased macroscopic IK amplitudes in a concentration-dependent way from 50 microM to 1 mM. The blocking effect was unchanged by repetitive depolarizing pulses and it was independent of the holding potential. Whereas activation of IK in control conditions was fitted by sigmoidal plus exponential time courses, only the sigmoidal time course gave an adequate fit with PR in the bath. The above effects were reversible. PR concentrations below 140 microM decreased single-channel activity for K+ channels with unitary conductance of 22 pS, in the voltage range between -40 and 60 mV from a holding potential of -50 mV. In contrast, the anaesthetic had nearly no effect on the opening probability of a channel with conductance of 10 pS. The unitary current amplitudes were unaffected in both channel types. These results suggest that PR action on IK may depend on the different blocking mechanisms of the K+ channels.

Haemodynamic effects of vecuronium.

Three hundred and twenty adults (ASA grade I, both sexes), received diazepam 10 mg by mouth (50% received atropine 7 micrograms kg-1 in addition) i.m. 45 min before operation. Patients were then allocated randomly to undergo general anaesthesia with either a nitrous oxide-neurolept technique or nitrous oxide-halothane. Vecuronium was administered to 50% of the patients in each anaesthetic group and heart rate and arterial pressure were monitored. Vecuronium did not influence heart rate, or systolic or diastolic arterial pressures.

Effective treatment of verapamil intoxication with 4-aminopyridine in the cat.

To study the value of 4-aminopyridine as an antidote to verapamil intoxication, we subjected 12 adult cats to verapamil poisoning by administering doses of 4.0-25.0 mg/kg verapamil by intravenous infusion. Six animals were given 4-aminopyridine 2 X 0.5 mg/kg i.v. after the verapamil infusion was stopped and the other six animals (the control group) were not. Verapamil caused profound cardiovascular depression and also partial neuromuscular block, both of which were completely reversed by 4-aminopyridine within 50 min, in spite of extremely high serum verapamil concentrations (ranging between 3,700 and 13,500 ng/ml). The six animals that received 4-aminopyridine survived the verapamil intoxication, whereas four of the six animals in the control group died. The results suggest that 4-aminopyridine may be useful in the treatment of verapamil intoxication.

Plasma protein concentration and recovery from anaesthesia in man.

The effect of the concentration of plasma protein on the recovery from anaesthesia induced by equipotent doses (UD95) of thiopentone and Althesin was studied in 48 patients. The recovery time (RT) wa plotted against the concentrations of total plasma proteins (TPP) and albumin (Al). A small decrease in TPP concentration from normal range affected the recovery time minimally; a small decrease in TPP concentration from a low basal value markedly increased the recovery time with both agents. A large decrease in TPP concentration increased the recovery time from thiopentone and Althesin markedly.

[Modified Ayre's T system for the elimination of environmental pollution]. / Un sistema a T di Ayre modificato per la eliminazione dell'inquinamento ambientale.

A modified Ayre T system for the elimination of anaesthetic gas and vapour pollution from operating theatres is described.

[Effect of proteinemia on recovery: a comparison between thiopentone and alphaxolone (althesin)]. / Effetto della proteinemia sul risveglio: confronto tra tiopentone ed alfaxolone (althesin).

The effect of proteinaemia and albuminaemia changes on recovery time following administration of an equipotent dose (DPC95) of thiopentone and alphaxolone has been evaluated. The study was carried out on two groups of 24 patients premedicated with atropine alone. Recovery time was more closely related to variations in albuminaemia compared to variations in total proteins: this results that albumins are the main binding-site of i.v. anaesthetics. Variations in total proteins and albuminaemia affect recovery time to a lesser extent when alphaxolone is used, compared with thiopentone. The result is related to the lower alphaxolone binding fraction. The clinical implications of protein binding fraction of anaesthetics is discussed.

[Elimination of anesthetic gases and vapors from operating rooms. System for passive conveyance of gases to the outside]. / Eliminazione di gas e vapori anestetici dalle sale operatorie. Il sistema a convogliamento all'esterno passivo.

Mathematical calculations were employed in an assessment of the resistances associated with a passive outward conveyance system for the removal of anesthetic gases and fumes from operating theatres. It was found that the magnitude of such resistances was not enough to interfere with the patient's respiratory dynamics.