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A Feltz

Publications and source records attributed to A Feltz.

At least 55 records · Page 3Linked to original sources
PubMed1989

Calcium currents in rat cerebellar Purkinje cells maintained in culture.

Calcium permeabilities were examined in large cerebellar neurons maintained in culture, and morphologically identified as Purkinje cells. When cells were supplied with a Dulbecco Minimum Eagle's Medium with 10% horse serum added (5-10 days), somatic recordings revealed complex spikes and these were shown to be generated by Na and Ca components, the Na one being tetrodotoxin-sensitive. At the dendritic level, Ca currents were better resolved than at the soma. In dendrites, Ca entry was shown to occur through at least two distinct currents. The first was a low-threshold transient current (elicited above -60 mV from a holding potential of -80 mV) which was reduced by almost 30% by 50 microM cadmium. The second was a high-threshold current (above -20 mV) which gave rise to (1) a transient component exhibiting a steady-state inactivation and so requiring holding potentials at -80 mV, and (2) a sustained component. Both components were suppressed by 50 microns cadmium. We measured a total Ca current at the dendritic level reaching values of up to 1 nA. In another culture medium (Leibovitz medium) known to allow expression of three types of calcium currents in nodose cells we observed the development of the dendritic tree of Purkinje cells but with no simultaneous expression of the high-threshold Ca current.

Action Potentials↗
PubMed1988

Dendrotoxin-sensitive K+ channels in dorsal root ganglion cells.

In primary sensory cells, a K current active at resting potential is selectively blocked by the convulsant snake toxin, dendrotoxin. Using the patch-clamp technique, we have examined the characteristics of this K current at the unitary level. The voltage-activated K+ channels were found to have a maximum conductance of 5-10 pS in a 'physiological' K+ gradient. They show negligible sensitivity to calcium at the inner membrane aspect. Blockade by dendrotoxin seems likely to be due to direct action on the K+ channel.

Animals↗
PubMed1988

Potassium currents in rat cerebellar Purkinje neurones maintained in culture in L15 (Leibovitz) medium.

Cerebellar Purkinje cells (PC) can be maintained in culture for one to two weeks in L15, a rich medium known to allow expression of a normal excitability in peripheral neurones. When examined using whole cell recordings, PC proved to be inexcitable in these conditions, and this inexcitability could be related to the presence of large outward K currents. Depolarizing steps of -100 mV revealed a voltage-dependent biphasic K current with a large early transient phase followed by a small plateau phase. The early transient phase could be selectively eliminated by holding the cell at -40 mV or by extracellularly applying 5 mM 4-aminopyridine (4-AP), whereas the plateau was abolished by 15 mM tetraethylammonium (TEA). Hereafter, these currents will be identified as the IA and the delayed current respectively, IA being the predominant current. IA activated between -25 and +65 mV with a midpoint at +3 mV; inactivation occurred between -70 and -20 mV with a midpoint at -57 mV. Current decay followed an exponential time course with a time constant of about 30 ms between -20 and +10 mV. In the cell-attached recording configuration, depolarization elicited openings of two types of K channels, one inactivating and one non-inactivating. The non-inactivating K channel probably corresponded to the delayed K current and had a conductance of 22 pS in a physiological K gradient.

4-Aminopyridine↗
PubMed1988

Small-conductance chloride channels activated by calcium on cultured endocrine cells from mammalian pars intermedia.

Porcine intermediate lobe (IL) endocrine cells maintained in primary culture have been studied using patch-clamp derived configurations to record unitary activity on outside-out vesicles. Solutions were devised so as to record Cl current in isolation and to fix cytoplasmic Ca concentration [Ca]i between 0.1 microM and 3 microM. Between [Ca]i 0.5 and 1 microM, the chloride permeability was restricted to single events with a small amplitude, that varied linearly with the membrane potential. Mean slope conductance of this chloride channel was 2.5 pS. Single channel analysis yielded two mean open time values of 10 and 55 ms at -80 mV. Relaxations of chloride currents on outside-out patches was examined at different [Ca]i. Relaxation was negligible at 0.15 microM [Ca]i, whereas at higher [Ca]i, the current exhibited relaxation in response to voltage jumps the kinetic of which could be fitted by two exponentials. At 0.5 microM [Ca]i, the fast relaxation time constant was shown to be voltage insensitive with a value of about 10 ms. The slow relaxation time constant had a mean value of 75 ms at -60 mV and increased with membrane depolarization with a twofold change over 120 mV. Another voltage effect was to favour the slow opening mode at the more depolarized potentials: the ratio of fast to slow relaxations being 5:1 at -60 mV as compared to 1:1 at +80 mV). Finally the estimated probability of opening (po) linearly increased with voltage. po displayed a bell-shaped dependence on [Ca]i, so that full activation of the channels was not achieved.

Animals↗
PubMed1987

Spontaneous and GABA-evoked chloride channels on pituitary intermediate lobe cells and their internal Ca requirements.

On porcine intermediate lobe (IL) endocrine cells, spontaneously opening chloride channels have been studied and compared to GABA-A activated chloride channels. Elementary currents were recorded mainly from outside-out patches excised from IL cells maintained in culture for 1-4 weeks. Spontaneous inward currents were observed in Cs-loaded cells after replacing Na in the extracellular medium by the impermeant ion choline. This activity, at an internal calcium concentration of 10(-8) M corresponded to a channel for chloride ions with a main conductance level of 26 pS, and substates around 11 pS. The sequence of permeabilities to halides was I greater than Br greater than Cl. These conductance characteristics were common to the GABA-operated channels which also showed a main conductance substate of 23-31 pS. The open time of the 26 pS level mostly encountered in spontaneous activity, was distributed along two modes: one, the most frequent, around 1 ms, and the other around 4 ms. This latter mode was the predominant one observed during GABA and isoguvacine applications but in addition a bursting activity of 19 ms duration was also seen. Specific GABA-A receptor antagonists (bicuculline and SR42641, 1 microM) blocked activity evoked by GABA (1-10 microM), but did not affect spontaneous events. These spontaneous Cl events were only observed in a restricted range of internal Ca concentrations, i.e. between 1 nM and 0.1 microM, and were practically abolished at Cai 1 microM. The GABA-induced activity of Cl channels was also Ca-sensitive, being reduced when Cai reached 1 microM.

Animals↗
PubMed1987

Intracellular effectors and modulators of GABA-A and GABA-B receptors: a commentary.

The inhibitory neurotransmitter GABA activates two receptor subtypes that can be distinguished by their pharmacology. The GABA-A site is competitively antagonized by bicuculline and exclusively coupled to a chloride channel. The GABA-B receptor, for which baclofen is the only specific agonist, is resistant to bicuculline inhibition and, depending upon its localization, will activate K currents and/or inhibit Ca currents. Both electrophysiological and biochemical approaches have been applied to the study of each receptor. The membrane and intracellular components that to date have been implicated in GABA-B activation are discussed: G proteins, adenylate cyclase and intracellular calcium levels. This latter factor is also discussed with respect to GABA-A receptor action.

Calcium↗
PubMed1986

Effect of internal calcium concentration on calcium currents in rat sensory neurones.

Using the patch-clamp technique in whole-cell configuration we have investigated the effect of increasing the internal calcium concentration (Cai) from below 10(-8) M to 10(-6) M on the three calcium currents: ICa,T (T for transient), ICa,S (S for sustained), ICa,N (N for neither), recently described in rat sensory neurones. Increasing Cai led to a dose-dependent reduction of the amplitude of ICa,S and, as Cai reached 5 X 10(-7) M ICa,S was nearly abolished. ICa,N is well evidenced from 5 X 10(-10) M to 10(-7) M where its is a large current. Preliminary observations indicate an increase of its inactivation rate following, as expected for a possible Cai dependent-inactivation, the increase of Cai from 5 X 10(-10) M to 10(-7) M. With Ca = 5 X 10(-7) M, all the cells displayed ICa,T and half of the cells in addition ICa,N, but it was of small amplitude. At Cai = 10(-6) M, most of the recorded cells only exhibited ICa,T.

Animals↗
PubMed1986

Inactivation of the low-threshold transient calcium current in rat sensory neurones: evidence for a dual process.

In rat cranial sensory neurones a transient Ca current (iCa,t) is elicited by depolarizing the membrane potential from -80 mV to beyond -50 mV. In this paper the characteristics of the slow and fast inactivation processes of this current are described. Recordings were obtained in whole-cell clamp conditions from Cs-loaded cells. For most experiments, cells were dialysed at an internal pCa of 8, and Na and K currents were eliminated using a choline chloride- and K-free external medium containing 5 mM-Ca and 2 mM-Mg. The decay of iCa,t could be approximately fitted by a single exponential with a voltage-dependent time constant which decreased from about 150 ms at -50 mV to about 25 ms at -20 mV. This suggests a single process of inactivation but a detailed kinetic analysis of the onset and the offset of the inactivation revealed biphasic processes. The onset of inactivation displays two exponential phases. The fast phase lasts for 100-500 ms, and the slow phase lasts for a few seconds. The relative amplitude and the time constants of each phase vary with the inactivating potential. The recovery from inactivation is also biphasic, with either a fast or a slow component predominating, depending on whether a short- (some hundreds of milli-seconds) or a long- (in the order of tens of seconds) inactivating pulse has been used. At -80 mV, after a 300 ms inactivating pulse, responses recover to at least 40% of maximum within 200 ms and recovery is complete within 1 s; after a long predepolarization (10-20 s), recovery takes 4-5 s. Fast recovery was observed best after large but brief depolarizations and slow recovery was observed best following long inactivating pre-pulses of small amplitude. The voltage-dependence of slow and fast inactivation was determined by realizing inactivation curves. Fast inactivation developed between -60 and -20 mV while the slow process occurred at more hyperpolarized potentials, e.g. at -75 to -50 mV. Fast inactivation was not altered by the entry of Ca during the previous activation of the channel. Further, decay of iCa,t was not modified when Ba was substituted for Ca or the internal pCa was decreased. These are indications of a uniquely voltage-dependent process. A possible role of Ca entry in slow inactivation is discussed.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1986

[Multiplicity of calcium permeabilities].

In this review, we deal with recent progress on calcium currents in neuronal membrane. Most of the results discussed have come from the use of the patch clamp technique which allows one to record currents of small amplitude (a few tens of pA in the whole-cell configuration or less than the pA with excised patches), and to impose a calcium gradient across the membrane. This allows access to the elementary currents and a pharmacology of the Ca channels is developed.

Animals↗
PubMed1985

IA current compared to low threshold calcium current in cranial sensory neurons.

Whole-cell recordings of cranial sensory neurons were obtained with CsCl- and tetraethylammonium (TEA)-loaded cells as used for ICa studies. When replacing calcium (Ca) with potassium (K) in the external medium, a transient inward current developed at low threshold, if the holding potential was below -100 mV. Its activation started above -60 mV and reached its maximum at -20 mV. Its reversal potential followed the predicted value of the K equilibrium potential (EK) characteristic of a K current. Pharmacologically, it resembles the classical outward A current since it is insensitive to TEA up to 20 mM and blocked by 4-aminopyridine (4-AP) and 3,4-AP in the millimolar range. This inward A current rises rapidly in less than 5 ms and decays monoexponentially with a time constant of about 60 ms at all potentials studied. Its steady-state inactivation occurred between -100 and -60 mV with a half-inactivation at -86 mV. All these characteristics hold for a voltage-dependent A current devoid of any Ca-dependent component. The activation and inactivation of this A inward current are compared to those of ICa,t, the other low threshold current encountered on those cells. The contribution of the two currents in the control of discharge frequency is discussed.

Aminopyridines↗
PubMed1985

Depolarization elicits two distinct calcium currents in vertebrate sensory neurones.

The calcium currents of rat sensory neurones (of the IX and X cranial nerves) grown in culture were studied using whole cell recordings. In cells loaded with CsCl, and bathed in a solution where Na was replaced by choline or Tris, a step depolarization from -80 mV to 0 mV elicited the well-documented sustained Ca current (iCa,s). In contrast, depolarization from -80 mV to -60 mV and up to -20 mV evoked a distinct transient inward current (iCa,t) which could be isolated by imposing an internal pCa 7. It relaxed in about 100 ms and could possibly occur independently of the former current. The transient current was only affected by manipulation of the Ca concentration in the external medium and therefore was considered to be also a transfer of Ca. Ba was shown to act as a substitute with a lower affinity than Ca. The maximal amplitude of this current was in the order of a few hundred pA in Ca 5 mM and Mg 2 mM. Both activation and inactivation occurred in the same voltage span. The underlying event was studied using noise analysis and compared to the Ca transfer occurring during the sustained current as measured in chromaffin cells by Fenwick et al. (1982). We found them to be of similar amplitude.

Animals↗
PubMed1985

Effect of taxol on secretory cells: functional, morphological, and electrophysiological correlates.

The effect of 0.5-1.0 microM taxol, a potent promoter of microtubule polymerization in vitro, was studied on the secretory activity of chromaffin cells of the adrenal medulla. Taxol was found to have a dual effect: the long-term effect (after a 1-h incubation) of taxol was to induce almost complete inhibition of catecholamine release, whereas after a short incubation (10 min) a massive, nicotine-independent release of catecholamine was produced. From results obtained using the patch-clamp technique to study the Ca++-dependent K+ channels (Ic channels), it was possible to conclude that taxol probably provokes an augmentation of free [Ca++]i in the cytoplasm, values increasing from 10(-8) M at rest to several 10(-7) M. The increased spontaneous release of stored neurohormones and the increased frequency of opening of Ic channels occur simultaneously and could both originate from a rise of [Ca++]i upon taxol addition. Immunofluorescence and ultrastructural studies showed that 13-h taxol treatment of chromaffin cells led to a different distribution of secretory organelles, and also to microtubule reorganization. In treated cells, microtubules were found to form bundles beneath the cell membrane and, at the ultrastructural level, to be packed along the cell axis. It is concluded that in addition to its action on microtubules, the antitumor drug taxol has side effects on the cell secretory activity, one of them being to modify free [Ca++]i.

Adrenal Medulla↗
PubMed1984

Patch-clamp study of the tetrodotoxin-resistant sodium current in group C sensory neurones.

Conditions were devised to isolate in cranial sensory neurones transfer of Na ions: K and Ca were omitted from the extracellular medium, and simultaneously cells were intracellularly loaded with 120 mM caesium and 20 mM TEA at [Ca]i = 10(-8) M. A tetrodotoxin (TTX)-resistant current was shown to be elicited by step depolarization from -25 MV upwards. This current successively activates and inactivates at increasing rates on further depolarization and at 0 mV (where peak amplitude is reached) its time course is of 20-50 ms. Absence of TTX-sensitivity (up to 15 microM), slow time course and an activation curve shifted by 15 mV towards the depolarized potentials differentiate this current from the more classical fast Na current which can be elicited on the same cells. Inactivation was provoked by a prepulse of varying amplitude and duration: with a prepulse command to -20 mV, inactivation was of 50% within a delay of 300 ms and almost 100% in about 1 min. After complete inactivation by command to 0 mV for 300 ms, recovery by holding the potential at -80 mV was of 50% in 205 ms, and of 100% after 1-4 s. It is concluded that a charge transfer of Na accounts for most of the hump which prolongs the action potential of these sensory neurones, and thus it can be proposed that spike duration as modulated by neurotransmitters may also involve Na in addition to Ca.

Animals↗
PubMed1982

Desensitization at the frog neuromuscular junction: a biphasic process.

1. The desensitization of the cholinergic receptor has been investigated at the frog neuromuscular junction. The agonist was either perfused or applied by ionophoresis.2. In all situations, desensitization develops in two phases: a fast one, experimentally in the second range but likely to be briefer, and a slower one, which extends over tens of seconds.3. When the presence of the agonist is prolonged, desensitization approaches a steady state, estimated through the amplitude of a test response. In steady-state conditions, this amplitude depends upon the desensitizing agonist concentration. The dose-response curve for desensitization induced by carbachol (CCh) indicates that half of the receptors can be desensitized at room temperature in the presence of 2.3 mum-CCh. The shape of the curve suggests that one desensitized receptor can bind two CCh molecules.4. The recovery from desensitization, estimated with a repetitive test pulse, displays two exponential phases. The time constant of the fast phase is 11-12 sec, and 4-5 min for the slow phase, regardless of the concentration or the nature of the agonist (acetylcholine or carbachol).5. The factor which most strikingly affects the relative amplitudes of the fast and slow phases of recovery is the duration of the (desensitizing) agonist application. Desensitizations lasting a few seconds are followed by a ;fast' recovery, whereas the slow phase of recovery is prominent when the agonist has been applied for more than 2 min.6. The fast and slow phases of desensitization onset and offset are not due to independent causes but are coupled: in given conditions, the onset can be essentially fast, and the recovery slow.7. All our findings can fit in a cyclic scheme of desensitization, derived from the one of Katz & Thesleff (1957) with two modifications: whether activatable or desensitized, one receptor molecule would have two agonist binding sites; moreover, the desensitized receptor would exist in two distinct and interconverting conformations: D(1), giving rise to the fast phases of onset and offset, and D(2), responsible for the existence of the slow components of desensitization.

Acetylcholine↗
PubMed1980

Interaction between nerve-related acetylcholine and bath applied agonists at the frog end-plate.

1. The interaction between acetylcholine (ACh) and carbachol (CCh) has been studied at the frog end-plate. The conditioning agonist, CCh, can cause desensitization (reduction of the ACh test response) and potentiation (increase of the test response). 2. Nerve-evoked end-plate currents (e.p.c.s), minature e.p.c.s and "slow" responses to ACh ionophoresis can all be potentiated by bath or ionophoretically applied CCh. 3. Since potentiation was found to be particularly visible at low temperatures, most experiments were performed at 5-8 degrees C. Potentiation results in an increase of both e.p.c. amplitude and e.p.c. decay time. Potentiated e.p.c.s teminate with a slow tail, the amplitude of which shows a high voltage sensitivity. Potentiation increases with CCh concentration (range studied 0-100 microM). It appears to persist throughout the application of CCh, even when desensitization is apparently the dominant phenomenon. 4. It is suggested that cross-potentiation of ACh by CCh results from the formation of intermediate non-conducting CCh-receptor complexes which have a high probability of being subsequently activated by ACh, yielding a conducting ACh-CCh-receptor complex. 5. Desensitization induced by fast bath application of CCh (or ACh) develops in two phases and can be fitted by the sum of two exponentials. Their time constants are in the second and the minute range, respectively. 6. The possibility that the slow phase is linked to the presence of agonist inside the cell is rejected.

Acetylcholine↗