Muscarinic inhibition of two potassium currents in guinea-pig prevertebral neurons: differentiation by extracellular cesium.

Muscarinic responses were studied in dissociated guinea-pig celiac ganglion neurons using the whole-cell voltage-clamp technique. Muscarine (0.025-1 mM; EC50 = 95 microM) administered to cells for 1.5 s evoked inward shifts in holding current in 53 of 74 cells. The amplitude of the inward current transients decreased with hyperpolarization and the null potential averaged -71 +/- 3.4 mV (n = 11). The currents that underlie the responses to muscarine were examined with hyperpolarizing voltage stepping protocols to -100 mV from a holding potential of -30 mV. Eighty-one per cent of cells displayed voltage-dependent current relaxations characteristic of the M-potassium current. Twenty per cent of responding cells displayed no M-current but only a voltage-independent current consistent with a leak current. In the latter type of cells, the muscarine-evoked inward currents reversed near EK and became outward at more hyperpolarized potentials. Analysis of steady state I-V relationships before and after bath application of muscarine showed that the two muscarine-sensitive potassium currents were distributed differently among three types of cells: (i) with M-current (18%); (ii) with leak current (18%); and (iii) with M-current and with leak current (64%). Cesium and barium were used to differentiate the M-current and the muscarine-sensitive leak current. Barium (2 mM) reduced the M-current and the leak potassium current, whereas cesium (2 mM) reduced the M-current but did not affect leak current. Thus, barium reduced the amplitude of muscarinic responses by 79% but cesium reduced them by only 14%. We conclude that muscarinic responses in guinea-pig celiac neurons are produced by suppression of two K+ currents: the M-current and a muscarine-sensitive leak current. These two currents are differentially susceptible to the potassium channel blockers barium and cesium.

CCKA receptors mediate slow depolarizations in cultured mammalian sympathetic neurons.

The effect of cholecystokinin octapeptide (CCK-8) was examined in guinea-pig celiac ganglion (CG) neurons in primary culture using standard intracellular recording techniques. Sulfated CCK-8 (CCK-8S; 1 microM) evoked slow depolarizing responses in 94% of CG neurons tested. In contrast, membrane potential was not affected by nonsulfated CCK-8 (CCK-8NS; 1 microM), CCK tetrapeptide (CCK-4; 1 microM), or gastrin (1 microM). The selective CCKA receptor antagonist L 364,718 potently inhibited CCK-8S-induced slow depolarizations (IC50 2.9 pM). In contrast, the selective CCKB receptor antagonist L 365,260 was a weak inhibitor of CCK-8S-induced slow depolarizations (IC50 1.3 microM). The depolarizing responses to CCK-8S were associated with an average increase in cell input resistance of 61%. Single electrode voltage clamp experiments indicated that CCK-8S-induced depolarizations were associated with a slow inward shift in holding current. Thus, the present findings indicate that guinea-pig cultured CG neurons are endowed with excitatory CCKA receptors the activation of which elicits a decrease in membrane conductance, thereby resulting in slow depolarizations.

Effect of (+)-sparteine on nicotinic acetylcholine receptors in the neurons of rat superior cervical ganglion.

The effects of (+)-sparteine, a ganglionic blocking agent, on acetylcholine (ACh)-induced membrane currents and on fast excitatory postsynaptic currents (EPSCs) were studied in the neurons of rat isolated superior cervical ganglion, with the whole-cell patch-clamp recording method and the two-electrode voltage-clamp method, respectively. (+)-Sparteine (2 microM) reduced the ACh-induced current caused by activation of nicotinic ACh receptors (AChRs) in a voltage-independent manner at membrane potentials of -50 mV to +30 mV, whereas its blocking effect increased at more negative membrane potentials. The dose-response relationship for ACh was modified by 2 microM (+)-sparteine at -50 mV and at -90 mV in a fashion typical for competitive rather than noncompetitive antagonists. The apparent mean open time of the AChR channel, as estimated from the power density spectrum of the ACh-induced current fluctuations at -90 mV, was not decreased by 2 microM (+)-sparteine, in contrast to what was observed with hexamethonium, the well known open-channel blocker for ganglionic AChRs. At higher concentrations, i.e., 5 microM and 10 microM (lower concentrations were not effective), (+)-sparteine reduced the amplitude of the EPSC and the time constant of the EPSC decay. The former effect was voltage independent, whereas the latter effect was voltage independent at membrane potentials of -70 mV and more positive and increased at membrane potentials of -90 and -110 mV. These results suggest that (+)-sparteine produces in ganglionic AChRs a competitive blocking effect and, in addition, an open-channel blockade. The latter component probably provides a smaller contribution than does the former to the blockade by (+)-sparteine of the ACh-induced current. Conformational analysis of the (+)-sparteine molecule was performed, and the dimensions of the molecule were measured. Minimum dimensions of the space-filling profile for two conformers, high and low populated, were found to be 7.3 x 7.9 A and 6.8 x 7.5 A, respectively. Both profiles are larger than the channel profile at which the open-channel blockers have been suggested to bind, which may explain comparatively low open-channel-blocking activity of (+)-sparteine.

[The tonic activity of single nerve fibers of the rabbit cervical sympathetic nerve]. / Tonicheskaia aktivnost' odinochnykh nervnykh volokon sheinogo simpaticheskogo nerva krolika.

Spontaneous sympathetic activity was recorded in single fibres dissected from the cervical sympathetic nerve trunk (CSNT) of rabbit. Conduction velocities and action potential amplitudes for B-fibres were measured in the whole nerve trunk. Results of the spectral analysis suggested that activity of unmyelinated fibres depended on baroreceptor activity to a greater extent than that of myelinated fibres and that the 2-3 Hz rhythm was present in animals with intact baroreceptors simultaneously with the cardiac rhythm. That rhythm was a usual feature of activity of both B- and C-fibres. Cross-correlation analysis of the single fibre activity was estimated in 24 fibre pairs. It was found that in five fibre pairs there was a correlation associated with the presence of a common physiological rhythm, in one fibre pair there was a correlation derived from the existence of a strong common input to both distinct preganglionic neurons.

[The periodic components of the integral tonic activity of the sympathetic nerves]. / Periodicheskie sostavliaiushchie integral'noi tonicheskoi aktivnosti simpaticheskikh nervov.

Sympathetic spontaneous activity in peripheral nerves of limbs and activity of C-fibres of the cervical sympathetic nerve trunk (CSNT) were recorded in situ from anaesthetized rabbits using multichannel coherent recording technique. Spectral characteristics of the activity and correlation between nerve activity and blood pressure were estimated. The data obtained have suggested that C-fibres in the CSNT are mainly vasoconstrictor fibres and their activity is more baroreceptor-dependent than that of sympathetic fibres in peripheral nerves. It is found that latencies of changes in the arterial blood pressure in response to changes in sympathetic activity are between 4 and 10 s.

[The mechanism of action of pachycarpine on the nicotinic cholinoreceptors of sympathetic ganglion neurons in the rat]. / Mekhanizm deistviia pakhikarpina na nikotinovye kholinoretseptory neironov simpaticheskogo gangliia krysy.

The mechanism of the pachycarpine action was studied in isolated superior cervical ganglion of rat using the patch-clamp method in the whole-cell recording mode. Action of the pachycarpine is not potential-dependent in the membrane potential range from +30 to -50 mV, the blockade increases during hyperpolarization of the membrane (-50-90 mV). Changes in the "dose-effect" dependence show that the blocking of nicotinic acetylcholine receptors is competitive both within the potential-dependent interval and within the potential-independent one.

Human sympathetic electrical activity recorded with skin surface electrodes.

Spontaneous electrical activity correlated to cardiac rhythm has been recorded with electrodes placed on the surface of the human arm or using the rabbit hindlimb. The signal-to-noise ratio has been improved using record averaging synchronized with the ECG. The recorded activity in man is a slow negative wave of sinusoid-like shape with a mean peak amplitude 0.08 +/- 0.03 microV. The sympathetic origin of this activity is suggested by the facts that its time course and conduction velocity are similar to those of integrated spontaneous electrical activity, recorded directly from postganglionic sympathetic fibers in the rabbit, and that it can be recorded from skin surface as a response to direct electrical stimulation of sympathetic nerve in the same animal.

[Tonic sympathetic activity in the sciatic nerve of the rabbit]. / Tonicheskaia simpaticheskaia aktivnost' v sedalishchnom nerve krolika.

Spontaneous sympathetic activity of tibial and peroneal nerves was investigated in anaesthetized rabbits using the multichannel coherent recording technique. The tonic activity of these fibres is shown to be mainly irregular. Sometimes it correlates with the cardiac rhythm. No modulation with 10 c/s frequency described by other researchers and no respiratory modulation are observed. At constant arterial pressure the amplitude of irregular changes in the nerve activity exceeded several times the average level of the activity.

[Study of the natural activity of nerve fibers using the method of multi-channel coherent recording]. / Issledovanie estestvennoi aktivnosti nervnykh volokon s pomoshch'iu metoda mnogokanal'nogo kogerentnogo priema.

Spontaneous electrical activity was recorded with a six channel amplifier from the intact vagal nerve (cervical area) of the cat in acute experiments. The records obtained were summated using different delays between them induced by a computer for differentiation of the afferent activity from the efferent one and estimation of the proper conduction velocity. It is found that the most active afferent fibres have conduction velocity about 25 m/s.