Membrane potential, conductance, and intracellular potassium concentration were measured in oligodendrocytes in 3-to lo-week-old cultures of embryonic mouse spinal cord. After intracellular recording the cells were first injected with Lucifer Yellow and then stained by immunofluorescence using rhodamine-labeled monoclonal antibody 01 specific for oligodendrocyte cell surfaces. The membrane potential of these identified oligodendrocytes was in mV -66 + 4.3 SD; it could be reversibly reduced almost to zero by the addition of ouabain. Changes in external K+ but not Na+, Ca++, or Cl-changed the membrane potential. A lo-fold increase in extracellular potassium concentration ([KQ depolarized the cell by about 52 mV. This is less than the 61 mV predicted by the Nernst equation for a K+ electrode assuming a constant intracellular potassium concentration ([K+]i).

We used intracellular microelectrodes to study the effects of hypoxia on the isolated, superfused sinoatrial (SA) node, atrium, and atrioventricular (AV) node of the rabbit heart. Hypoxia decreased the rate of spontaneous impulse initiation in SA nodal fibers by decreasing the slope of diastolic depolarization. With gradually decreasing Po2, the sinus rate was reduced; concomitantly, the corrected sinus node recovery time after rapid atrial stimulation was much less affected demonstrating marked prolongation only under severe anoxic conditions. Hypoxia decreased the amplitude of action potentials of the SA node and of the AV node but not of the atrium. SA and AV nodal conduction were slowed by hypoxia; intraatrial conduction was not significantly affected. AV nodal conduction block occurred at lower atrial rates, and the effective refractory period of the AV node was prolonged. Inhomogeneity of SA and AV nodal impulse propagation often was observed in the presence of hypoxia. This was associated with concealed reentry within both nodal areas. The extracellular K+ concentration of the atrial tissue was measured with ion-sensitive microelectrodes. [K+]o remained unchanged even after prolonged periods of severe hypoxia. These results are consistent with the hypothesis that acute hypoxia predominantly inhibits slow response activity but has only little effect on the fast inward sodium current.

In 34 cats, the changes in extracellular potassium ion activity (aK) and extracellular spike activity within the pool of respiratory neurones in the dorsormedial and ventrolateral medulla were recorded using microelectrodes filled with a liquid potassium ion exchange resin. Cyclic changes in aK which parallel central respiratory activity were restricted to those regions where respiratory neurones are known to be localized. The largest changes in aK (0.1--0.3 mmol . 1(-1)) were found within the ventral pool of inspiratory neurones. The aK increased during inspiration in parallel with the pattern of phrenic nerve activity. The smallest changes in aK (0.02--0.06 mmol . 1(-1)) were observed within the ventral pool of expiratory neurones. Here, aK showed a transient increase during both inspiration and expiration. Within the dorsal pool of inspiratory neurones, small fluctuations of aK were observed paralleling phrenic nerve activity and the afferent discharge of the intact vagal nerves. After the vagal nerves were cut, the changes in aK then paralleled phrenic nerve activity. The variations in aK within the ventral pool of respiratory neurones did not change after bilateral section of vagal nerves. Repetitive stimulation of the vagal nerves (0.1--0.5 V, 0.05 ms) produced an increase in aK only within the dorsal pool of inspiratory neurones, whereas repetitive spinal cord stimulation (5--10 V, 0.05 ms) resulted in an increase of aK within the ventral pool of respiratory neurones. The amplitude of the cyclic changes in aK increased significantly whenever the electrode approached individual respiratory neurones as verified by the amplitude and shape of the spikes recorded by the reference barrel. The maximal changes in aK then reached a peak amplitude of 1.3--1.5 mmol . 1(-1), the pattern of aK changes resembling that measured within the pools of neurones. The aK started to rise prior to the discharge of action potentials, indicating that the efflux of K + -ions was produced as a consequence of synaptic transmission. The functional importance of these changes in extracellular potassium is discussed.

The kinetic reactions of a voltage-dependent K+ channel, which constituted about 14% of all the recorded K+ channels in the membrane of cultured rat astrocytes were studied in detail. A scheme of one open and three closed states is necessary to describe the kinetic reactions of this channel. The channel contributes little to the resting membrane potential. Its steady state open probability (Po) is 0.06 at -70 mV. When the cell is depolarized to O mV, Po approaches 1. This represents a 17-fold increase. Such channels could contribute to the potassium clearance by enhancing the effect of "spatial buffering." Additionally, single anion-selective channels with very high conductances were found in inside-out patches in approximately 15% of all recorded channels in the membrane of rat astrocytes. Channel openings are characterized by more than one conductance level; the main level showed a mean conductance of 400 pS. These channels are divided into two groups. Approximately 90% of the recorded chloride channels showed a strong voltage dependency of their current fluctuations. Within a relatively small potential range (+/- 15 mV) the channels have a high probability of being in the active state. After a voltage jump to varying testing potentials in the range of +/- 20 to +/- 50 mV the channels continued to be in the active state for some time and then closed to a shut state. If the testing potential persisted, the channels were not able to leave this shut state.(ABSTRACT TRUNCATED AT 250 WORDS)

A small angle stepping motor was used for construction of a micropositioner. Linear movements are produced by direct coupling of the rotor axis to high precision microdrive. The linearly moving system is constructed from stainless steal prismatic guides with hardened surfaces and permits precise steps in the 100 nm range. Extreme reduction of the moving masses and minimal friction of the radial thrust bearing enables strong acceleration of the electrode. During simultaneous measurements of step performance motoneurons in the frog spinal cord, CA 1 cells of hippocampal brain slices and glia cells in tissue culture were punctured with single electrodes (tip less than l micron and double barrelled ion-sensitive microelectrodes (phi 1,5-2 micron). In all three preparations, cell penetration could be performed by means of both types of electrodes with a high yield when the step velocity reached or exceeded 4 mm/s. Steps with lower velocity resulted in less successful cell penetrations and were accompanied by typical dimpling effects. The results indicate that a critical velocity is required for cell puncturing with a minimum of damage.