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A Trautmann

Publications and source records attributed to A Trautmann.

At least 73 records · Page 4Linked to original sources
PubMed1989

Arachidonic acid closes gap junction channels in rat lacrimal glands.

The effects of arachidonic acid (AA) on gap junction conductance of rat lacrimal glands have been studied with the double patch-clamp technique. Extracellular application of 50-100 microM AA for a few minutes induced a closure of gap junction channels. This effect was mimicked by linoleic acid and by other non-degradable fatty acids (myristic and lauric), and was not blocked by inhibitors of AA metabolism. This suggests that the active molecule was the fatty acid itself, and not one of its oxidative derivatives. Inhibitors of AA metabolism caused a certain degree of uncoupling by themselves, probably due to the accumulation of AA. This effect was reduced in the presence of 10 microM 4-bromophenacylbromide, an inhibitor of phospholipase A2. The effect of AA did not seem to be mediated by an increase of intracellular Ca concentration, nor by a change in the activity of guanylate or adenylate cyclases, nor by activation of protein kinase C. Therefore it could be attributed to a direct effect of AA on gap junctions. Analysis of single gap junction channel currents showed that AA-induced closure of these channels resulted from a change in the number of open channels, and not from a reduction of their conductance. Finally, acetylcholine-induced closure of gap junction channels was not primarily mediated by an increase in AA concentration, although such an increase may well follow the activation of muscarinic receptors and play a role in the acetylcholine effect.

Acetophenones↗
PubMed1989

Effects of calcium ion on neurite outgrowth of rat spinal cord neurons in vitro: the role of non-neuronal cells in regulating neurite sprouting.

The interactions of nerve cells with their environment and other cells are specific to different stages of cellular differentiation. Neurite outgrowth was measured from cultured spinal cord neurons under the influence of different Ca2+ concentrations. We used fluorodeoxyuridine (FuDr), an antimitotic agent which reduces significantly the proportion of non-neuronal cells in spinal cord cell cultures, to examine the effects of non-neuronal cells on neurite outgrowth. Spinal cord neurons responded to changes in their environment by means of two types of neurite outgrowth: sprouting and elongation. The concurrent presence of non-neuronal cells led to increased sprouting of neurites in certain ionic environments, thus lending support to the idea that non-neuronal cells release diffusible factors which influence sprouting and guide neurite outgrowth.

Animals↗
PubMed1988

Calcium and secretagogues-induced conductances in rat exocrine pancreas.

The electrical properties of single acinar cells isolated from rat pancreas were studied with the whole-cell tight-seal recording method. Under resting conditions, the relative permeabilities of Cl and K were PCl/PK approximately equal to 3. At 1 microM internal calcium, a Ca and voltage-dependent Cl conductance was activated. At 10 microM internal calcium, the major conductance was selective for cations. It was not voltage-dependent. Acetylcholine and cholecystokinin induced an increase of internal Ca which in turn activated either only a Cl conductance or both Cl and cationic conductances. The secretagogue-induced conductance was increased to a variable extent by depolarisation. The absence of K channels activated by internal calcium indicates that, in pancreatic acinar cells, the mechanism of fluid secretion differs from that observed in other exocrine glands.

Acetylcholine↗
PubMed1988

Acetylcholine-induced closure of gap junction channels in rat lacrimal glands is probably mediated by protein kinase C.

In rat lacrimal gland cells, application of acetylcholine (ACh) opens Ca-dependent channels and closes gap junction channels. We have shown previously that the increase in intracellular calcium concentration induced by ACh, is not required for the closure of gap junctions. We have examined the effects of activators of protein kinase C on gap junction conductance measured with the double patch-clamp technique. This conductance was markedly reduced by incubating the cell pairs for a few minutes with 100 nM phorbol dibutyrate (PdBu). Two membrane permeant analogues of diacylglycerol, OAG (1-oleoyl-2-acetyl-glycerol) and DOG (1,2-dioleoyl-glycerol) also induced a closure of gap junction channels. This effect was observed in the concentration range 10-100 microM when the diacylglycerol was added on intact cells, and at 75 microM when it was applied on dialysed cells. The cell uncoupling was not mediated by phosphatidate, a degradation product of OAG, nor by a phospholipase A2-induced increase in arachidonate concentration. The OAG-induced closure of gap junction channels reversed spontaneously upon prolonged exposure (more than 90 min at 37 degrees C) to 25 microM OAG. After a prolonged OAG treatment, the ability of ACh to uncouple the cells was markedly reduced. ACh induced uncoupling was modulated to some extent by intracellular Ca and had an absolute requirement for Mg. These results indicate that ACh-induced closure of gap junction channels may be mediated by PKC.

Acetylcholine↗
PubMed1987

Ionic channels in murine macrophages.

In this paper we examine the different voltage or calcium-dependent currents present in murine peritoneal macrophages, and in a macrophage-like cell line, J774. Three of these are K currents while the fourth is carried by Cl. One K current, activated by hyperpolarization, has all the characteristics of the inward rectifier found in egg or muscle cells. It appears in peritoneal macrophages only after several days in culture. A second K current, activated by depolarization, is a typical delayed rectifier. The amplitude of these currents and, as a consequence, the membrane potential of the cells, can be markedly changed by the movement of fluid around the cells. A third K current is activated by internal calcium levels in the micromolar range. It presents a low-voltage sensitivity and is blocked by 0.1-1 mM quinine. The Cl current flows through large-size channels (180-390 pS) that are active mainly in excised patches. These channels are unlikely to be half gap junctional channels, as suggested in former studies. The second goal of this paper is to examine if the activation of receptors for the Fc fragment of IgGs (Fc receptors) is associated with a change in the electrical properties of the membrane of macrophages. We have observed that the binding of multivalent ligands (the monoclonal antibody 2.4G2, aggregated IgGs, or sheep red blood cells coated with IgGs) to their Fc receptors on adherent macrophages did not trigger any change in resting potential. This is a surprising difference with former results obtained on non-adherent J774 cells (Young, J. D.-E., J. C. Unkeless, H. R. Kaback, and Z. A. Cohn, 1983, Proc. Natl. Acad. Sci. USA., 80:1357-1361) and on human alveolar macrophages (Nelson, D. J., E. R. Jacobs, J. M. Tang, J. M. Zeller and R. C. Bone, 1985, J. Clin. Invest., 76:500-507).

Animals↗
PubMed1986

Blockage of Ca-activated Cl conductance by furosemide in rat lacrimal glands.

Single cells isolated from rat lacrimal glands were studied with the tight-seal whole-cell recording technique. It was found that furosemide (1 mM, applied externally) selectively blocked one part of the electrical response elicited by muscarinic agonists. This component of the response had been shown in a previous work (Marty et al. 1984) to be due to Ca-dependent Cl channels. The action of furosemide was further studied on cells which were dialysed with a high-Ca, high-Na solution, and which mainly displayed the Ca-dependent Cl conductance. In these experiments, furosemide (1 mM) was again found to depress the Ca-dependent Cl current. The present findings offer an explanation for previous reports that furosemide blocks ion fluxes and electrolyte secretion in exocrine glands without necessarily involving the neutral Na-K-Cl carrier usually assumed to be affected by the drug.

Animals↗
PubMed1986

Voltage-dependent channels of human muscle cultures.

Cultures were grown from satellite cells obtained from biopsies of normal children and of boys having Duchenne muscular dystrophy (DMD). Patch-clamp recordings were obtained from mononucleated cells and from young myotubes containing up to five nuclei. Four current types were distinguished. Na currents had a maximum amplitude near -10 mV and a half inactivation point near -60 mV. Single channel currents observed in isolated patches had a main unit size of 1.8 pA at -30 mV. Voltage dependent outward K currents were blocked by applying tetraethylammonium to the bath solution. In some cells, outward currents had a rather slow activation and did not inactivate. In other cells, activation was faster, and the currents inactivated. At large positive potentials, another K current was activated. The corresponding channels displayed large unit steps in isolated patches. Hyperpolarizing voltage pulses elicited in about one third of the cells inward rectifier currents. All currents types were found with similar characteristics in normal and DMD cultures. Whole cell results were very variable. Cells displayed various combinations of the four kinds of currents. To understand the origin of this diversity, clonal cultures were investigated. Clones displayed more homogeneous electrical properties than standard cultures, suggesting the presence of various types of stem cells in the non-clonal cultures.

Adolescent↗
PubMed1986

Acetylcholine receptors are not functionally independent.

Analysis of current recordings from acetylcholine-activated channels has largely rested so far on the hypothesis of independence, which states that the opening of one channel does not influence that of its neighbors. We have submitted this assumption to several tests, using as experimental material single channel currents from rat myotubes. We found that, even though the distribution of multiple channel openings may be approximated by the Poisson law, openings are strongly coupled. This conclusion is derived from the analysis of two-time properties associated with patch-clamp data. We show how these properties, which contain more detailed information than the stationary probabilities, can be calculated in practice and why a Poisson analysis is misleading in the present case. The implications of our findings are finally discussed in terms of channel structure and function.

Animals↗
PubMed1986

Acetylcholine modulation of the conductance of intercellular junctions between rat lacrimal cells.

The conductance of intercellular junctions between rat lacrimal cells was studied with the double whole-cell tight-seal recording technique. This conductance decreases spontaneously with time as a result of the double-cell dialysis. The rate of this 'spontaneous' uncoupling is unaffected by changing the internal Ca concentration, [Ca]i, between 10(-8) M and 10(-6) M. This rate of uncoupling is greatly increased when [Ca]i is approximately 10(-5) M, and this effect does not involve changes in the internal proton concentration. When [Ca]i is weakly buffered in one of the two cells, 1-2 microM-acetylcholine (ACh) both activates Ca-dependent channels in that cell (Marty, Tan & Trautmann, 1984) and uncouples the two cells. The uncoupling is not synchronous with the increase in [Ca]i as reflected by the Ca-dependent currents. When [Ca]i is strongly buffered in both cells, ACh fails to activate Ca-dependent currents, but it can still uncouple the cells. This ACh-induced uncoupling is often preceded by a transient enhancing of the coupling. In conclusion, ACh has several distinct effects on lacrimal cells: activation of Ca-dependent channels in the plasma membrane, closure of junctional channels involving a Ca-independent mechanism, and sometimes, an increase in the junctional coupling by a Ca-independent mechanism.

Acetylcholine↗
PubMed1986

Muscarinic response in rat lacrimal glands.

A large variety of responses has been uncovered by recent investigations of conductance changes elicited by muscarinic agonists. In exocrine glands, the permeability to K+, Cl- and Na+ ions is increased, and internal Ca2+ serves as a second messenger. Patch-clamp analysis of the secreting cells has revealed three types of Ca2+-dependent channels, which are respectively selective for K+, for Cl-, and for monovalent cations. The channels differ in their sensitivity to the internal Ca2+ concentration, Cai. K+-selective channels are partially activated at rest, with Cai approx. 10 nmol l-1; Cl(-)-selective channels are activated between 100 nmol l-1 and 1 mumol l-1; activation of cationic channels requires micromolar Cai levels. Cell-attached recordings, performed either on isolated cells or on cell clusters, show an activation of all three channel types upon application of acetylcholine. In whole-cell recordings, mostly K+- and Cl(-)-selective channels are activated. The cell currents display slow oscillations linked to variations of Cai. Whole-cell currents rise after a delay of approx. 1 s, and decay with a time constant of approx. 0.7 s upon removal of acetylcholine. They do not depend on extracellular Ca2+. The recent demonstration that Ca2+-dependent currents can also be obtained when dialysing the cells with inositoltrisphosphate or with GTP gamma S, a non-hydrolysable analogue of guanosine triphosphate, opens promising leads to an analysis of intracellular events regulated by acetylcholine.

Acetylcholine↗
PubMed1986

Physiological modulation of gap junction permeability.

In many tissues cells communicate directly through arrays of intercellular channels which are organized to form gap junctions. These channels are permeant to inorganic ions as well as to small hydrophilic molecules up to Mr 2000. The electrical and chemical coupling provided by such junctions is under the control of intracellular and, in many cases, extracellular substances. The latter (hormones or neurotransmitters) function via the activation of intracellular second messengers. These can rapidly affect the state of opening of the junctions, or induce long-term modulation of the coupling. What are the second messengers and how do they control the functional state of the junctions? These questions' remain largely unanswered, although several internal molecules are thought to be involved in these modulations (e.g. Ca2+, H+ or cyclic AMP). The double patch-clamp technique which enables control of both the intracellular milieu and high resolution measurement of transjunctional currents, has recently been applied to study these problems. In particular, it is now possible to examine at the single channel level how junctional conductance is modulated in terms, for example, of the number of open channels or channel elementary properties.

Animals↗
PubMed1984

Incorporation of chromaffin granule membranes into large-size vesicles suitable for patch-clamp recording.

Incubation of chromaffin granules with excess liposomes at pH 6.0 resulted in the formation of cell-size structures, which were purified by centrifugation on sucrose gradients. Experiments with fluorescein-labeled granules indicated incorporation of granule membrane to these structures. The preparation contained various vesicular structures with a diameter up to 15 micron. The largest elements were studied by the 'patch-clamp' technique. 'Cell-attached' and 'whole-cell' recordings indicated the presence of currents corresponding to unitary conductances ranging from 100 to 500 pS.

Animals↗
PubMed1984

Single acetylcholine-activated channel currents in developing muscle cells.

The properties of single acetylcholine-activated ion channels in developing rat myoblasts and myotubes in tissue culture have been investigated using the gigaohm seal patch clamp technique. Two classes of ACh-activated channels were identified. The major class of channels (accounting for greater than 95% of all channel openings) has a conductance of 35 pS and a mean open time of 15 msec (at room temperature and -80 mV). The minor class of channels has a larger conductance (55 pS) and a briefer mean open time (2-3 msec). Functional ACh-activated channels are present in undifferentiated mononucleated myoblasts 1-2 days in culture, although the channel density on such cells is low. Over the next week in culture, as the myoblasts fuse to form multinucleate myotubes, there is a marked increase in channel density and an increase in the proportion of large conductance channels. No significant change, however, occurs in channel conductance or open time (within a given class of channels) during this period. At high concentrations of ACh, channels desensitize and channel openings occur in groups, similar to what has been previously described in adult muscle. The rate of channel opening within a group of openings increases with increasing agonist concentration while mean open time is independent of agonist concentration, as expected from simple models of drug action. During a group of openings, the channel is open for half the time (i.e., channel opening rate is equal to channel closing rate) at a concentration of approximately 6 micron ACh.

Acetylcholine↗
PubMed1984

Activation of Ca-dependent K channels by carbamoylcholine in rat lacrimal glands.

Electrical properties of the membranes of lacrimal gland cells were investigated using patch-clamp techniques [Hamill, O.P., Marty A., Neher, E., Sakmann, B. & Sigworth, F.J. (1981) Pflügers Arch. 391, 85-100]. The membranes were found to contain a specific kind of voltage- and Ca2+ -activated K+ channel ("BK channels"). These channels account for the strong rectification of the cell current-voltage curve as obtained in tight-seal whole-cell recordings. Application of low concentrations of carbamoylcholine (CbmCho, 0.5 microM) activated the BK channels. No effect was obtained in the presence of atropine (2 microM) or when dialyzing the cell with a strong CaEGTA buffer. The latter result, together with other findings, suggests that CbmCho exerts its action on BK channels by increasing the intracellular Ca2+ concentration. This Ca2+ concentration increase presumably occurred via liberation from a cytoplasmic Ca2+ store, because the response remained unaffected in the absence of extracellular Ca2+. At higher CbmCho concentration (2 microM), an inward current was observed, which was assumed to result from activation of another type of Ca2+ -regulated channel.

Acetylcholine↗
PubMed1984

A patch-clamp study of the partial agonist actions of tubocurarine on rat myotubes.

Single channels activated by (+)-tubocurarine (curare) were recorded from rat myotubes using the patch-clamp technique. The agonist-like action of curare does not result from a contaminant molecule, as the same effects were observed with curare purified by high-performance liquid chromatography. A curare-activated channel can adopt two levels of conductance: full (F) or partial (P). The F state has a slope conductance of 40 pS (identical to that of the acetylcholine (ACh)-activated channel) and the P state has a conductance of 13 pS. At low concentrations of agonist (ACh or curare), the distribution of channel open times is biphasic. The briefer channels may result from the binding of a single agonist molecule whereas the longer-lived channels probably occur following the binding of two agonist molecules. The mean open time of the F state decreases with increasing curare concentration. It is shown that band-width limitations are likely to account for only a very small part of this observed reduction. In contrast, the mean open time of the P state is independent of the concentration of curare. A simple interpretation is that the F state is susceptible to channel blockade by curare, whereas the P state is not. The P state preceded the F state almost as often as it followed the F state; it can also be observed separately from the F state. The fraction of events including a P state increases from about 4% in the presence of 1 microM-curare to 30% at 100 microM-curare. This fraction is also increased by hyperpolarization. When the curare concentration is increased, the F-state frequency first increases and then decreases at higher concentration. This frequency is also decreased by hyperpolarization. The decrease in F-state frequency is probably related to channel blockade by curare; it cannot be wholly accounted for by problems associated with limited time resolution. A synthetic analogue of curare, (+)- tubocurine dimethiodide presents an agonist activity similar to that of curare but with a faster closing rate for both F and P states. The various actions of curare are summarized in two possible models where the P state is interpreted as either a partially open channel or a channel which is partially blocked.

Acetylcholine↗
PubMed1984

Three types of calcium-dependent channel in rat lacrimal glands.

Isolated cells from rat lacrimal glands were studied with patch-clamp techniques. Whole-cell and cell-attached recordings were obtained while the cells were stimulated by application of carbamylcholine or of the Ca ionophore, A23187. The results were compared with recordings of Ca-dependent channels obtained in isolated patches. Whole-cell recordings revealed two types of carbamylcholine-induced current. At low levels of stimulation, a specific class of Ca-dependent K channels was selectively activated ('BK channels'). With more intense stimulation an inward current, Ii, was obtained at the cell resting potential. Ii rose rather abruptly after a long delay. In several cells, Ii currents presented spontaneous oscillations. Both K and Ii current responses to carbamylcholine were due to activation of muscarinic receptors. Both responses were elicited by a rise of the intracellular Ca concentration. The immediate source of Ca was intracellular. Replacement of intracellular K with either Na or Cs blocked BK channels entirely, thus allowing the study of Ii currents free from K currents. Ii responses to carbamylcholine were, however, less frequently obtained in Na- or Cs-dialysed cells than in K-dialysed cells. In symmetrical NaCl solutions, Ii inverted at 0 mV. When replacing part of the intracellular or extracellular Cl with glutamate the reversal potential, Ei, was found to vary in the same direction as the equilibrium potential for Cl ions, ECl. In some experiments, Ei was close to ECl but in others Ei deviated strongly from ECl. These experiments suggested that Ii was mainly due to a Cl-selective conductance, and that another conductance type was contributing to Ii in variable proportions. It was found that, in K-free solutions, Ii had a reversal potential very close to ECl. Noise analysis showed that the Cl channels involved in Ii current had a unit conductance of about 1-2 pS in symmetrical NaCl solutions. At -60 mV, the mean channel open time derived from noise power spectra was about 200 ms. The activation of the Ca-dependent Cl channels was increased by depolarization. Voltage jumps elicited slow exponential relaxations. At -60 mV, the time constants of the relaxations were in the range 100-250 ms. Cell-attached recordings suggested that internal Ca activated three types of channel, depending on the Ca concentration: BK channels, 2-4 pS channels and 25 pS channels. Inside-out and outside-out patch conditions allowed a rough estimate to be made of the Ca concentration needed to activate each class of channel.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1983

A comparative study of the activation of the cholinergic receptor by various agonists.

At the frog neuromuscular junction, a dose-response curve for the activation of the nicotinic receptor by carbachol has been determined under conditions where desensitization could be estimated and corrected for. The value of the Hill coefficient was 2 and that of the dissociation constant for carbachol was 400 microM, the two binding sites of the receptor being assumed identical. The properties of six cholinergic agonists were then compared. the potencies and mean open times of these agonists are ranked in the same order, but the range of the potencies is much larger (1-200) than that of the mean open times (1-4). The differences in the properties of the different agonists could simply be due to differences in the rate of dissociation of the agonists, if it is assumed that one apparent opening of the channel is in fact a burst of several oscillations between the open and closed conformations, such that a burst is interrupted by the dissociation of one agonist molecule.

Animals↗