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F Ramón

Publications and source records attributed to F Ramón.

At least 19 recordsLinked to original sources
PubMed1991

Humoral factors reduce gap junction sensitivity to cytoplasmic pH. I. Organ ablation studies.

The sensitivity of gap junctions connecting crayfish lateral axons to uncoupling by axoplasmic acidification was studied after altering the hormonal balance of animals by 1) ablation of eyestalks or sinus glands or 2) inducing long-lasting defensive posturing behavior (stress). Internal pH (pHi) was measured with microelectrodes, and junctional resistance (Rj) was calculated from input and transfer resistances. In isolated nerve cords from intact animals, the maximal Rj (Rjmax) reached after acidification varied diurnally (Rjmax approximately 10 and 0.6 M omega at 0900 and 1800 h, respectively). Basal Rj (20-30 k omega) did not change during the 24-h period. Organ ablation (eyestalks or sinus glands) or stress rendered gap junctions less sensitive to uncoupling by low pHi within 1 h or 2 days; recovery toward control values had different time courses. The reduced pH sensitivity of crayfish junctions seen after eyestalk ablation is attributable to stress in its early phase (lasting 1-2 days) and to ablation of the endocrine organs in its late phase (2-7 days). No striking structural differences accompanied these changes, indicating that the altered properties are not due to major changes in gap junction expression.

Animals↗
PubMed1991

Humoral factors reduce gap junction sensitivity to cytoplasmic pH. II. In vitro manipulations.

Our previous studies demonstrated a diurnal rhythm in the response of gap junctions between crayfish giant axons to acidification and that the response was reduced after eyestalk ablation, sinus gland removal, or visual stress. In this paper we describe experiments to test whether compounds in the circulating hemolymph were responsible for modulation of the responsiveness gap junction channels to intracellular pH. In axons from destalked animals in which the hemolymph had been replaced with normal saline, the maximal junctional resistance after acidification (Rjmax) reached control values. In contrast, Rjmax reached only 30% of control after acidification in axons from animals that had been destalked but not perfused. Hemolymph drawn after eyestalk ablation was tested on axons from control animals. Treatment with hemolymph drawn 1 day after destalking resulted in control Rjmax values, while treatment with hemolymph drawn 7 days after destalking resulted in Rjmax values of only 5-40%. Similarly, pretreatment for 1 h with 100 microM ecdysterone resulted in low Rjmax values. These experimental results suggest that a circulating compound, most likely ecdysterone or a related molecule, regulates the physiological properties of gap junctions from crayfish lateral axons.

Animals↗
PubMed1990

Protein phosphorylation and hydrogen ions modulate calcium-induced closure of gap junction channels.

The regulation of the cell-to-cell pathway formed by gap junctions seems to involve the interaction of the junctional channels with either calcium or hydrogen ions, as well as protein phosphorylation and calmodulin. These mechanisms of junctional regulation have been considered to act independently on specific sites of the gap junction protein; however, the possibility that they may be interrelated has not been adequately explored mainly due to the difficulties involved in simultaneous measurement of intracellular cations and protein phosphorylation. To further understanding of mechanisms regulating gap junctions, we have internally perfused coupled lateral axons from crayfish with solutions containing different calcium and hydrogen concentrations under conditions favoring phosphorylation, while monitoring the junctional conductance. We found that calcium ions regulate cell communication probably through a direct interaction with the channel protein. Phosphorylation and low pH do not alter junctional conductance themselves, but appear only to modulate the effects of calcium, possibly by altering the affinity of the channel for calcium. We propose that a combination of free intracellular calcium and protein phosphorylation form an important physiological mechanism regulating intercellular communication.

Animals↗
PubMed1988

Calmodulin acts as an intermediary for the effects of calcium on gap junctions from crayfish lateral axons.

Lateral axons from the abdominal nerve cord of crayfish were internally perfused with the calcium receptor calmodulin (CaM) in solutions with low (pCa greater than 7.0) or high (pCa 5.5) calcium concentrations and studied electrophysiologically and morphologically. Results from these experiments show that when the internal solution contains calcium-activated calmodulin (Ca2+-CaM) the junctional resistance between the axons increases from control values of about 60 to 500-600 k omega in 60 min. In contrast, axons perfused with calmodulin in low calcium solutions maintain their junctional resistance at control levels during the 60-min perfusion. Similar results are obtained when only one or both coupled axons are perfused. The morphological study shows that in the perfused axons the axoplasmic organelles are replaced or grossly perturbed by the perfusion solution up to the region of the synapses. Additionally, in axons perfused with Ca2+-CaM there are regions where the synaptic gap between the membranes decreases from a control 4-6 to 2-3 nm. Both electrophysiological and morphological results can be interpreted as indicating that calcium-activated calmodulin acts directly on the junctional channels to induce their closure.

Animals↗
PubMed1988

Structural characteristics of gap junctions. I. Channel number in coupled and uncoupled conditions.

Gap junctions between crayfish lateral axons were studied by combining anatomical and electrophysiological measurements to determine structural changes associated during uncoupling by axoplasmic acidification. In basal conditions, the junctional resistance, Rj, was approximately 60-80 k omega and the synapses appeared as two adhering membranes; 18-20-nm overall thickness, containing transverse densities (channels) spanning both membranes and the narrow extracellular gap (4-6 nm). In freeze-fracture replicas, the synapses contained greater than 3 X 10(3) gap junction plaques having a total of approximately 3.5 X 10(5) intramembrane particles. "Single" gap junction particles represented approximately 10% of the total number of gap junction particles present in the synapse. Therefore, in basal conditions, most of the gap junction particles were organized in plaques. Moreover, correlations of the total number of gap junction particles with Rj suggested that most of the junctional particles in plaques corresponded to conducting channels. Upon acidification of the axoplasm to pH 6.7-6.8, the junctional resistance increased to approximately 300 k omega and action potentials failed to propagate across the septum. Morphological measurements showed that the total number of gap junction particles in plaques decreased approximately 11-fold to 3.1 X 10(4) whereas the number of single particles dispersed in the axolemmae increased significantly. Thin sections of these synapses showed that the width of the extracellular gap increased from 4-6 nm in basal conditions to 10-20 nm under conditions where axoplasmic pH was 6.7-6.8. These observations suggest that single gap junction particles dispersed in the synapse most likely represent hemi-channels produced by the dissasembly of channels previously arranged in plaques.

Animals↗
PubMed1986

Lowering of pH does not directly affect the junctional resistance of crayfish lateral axons.

The effect of pH was tested on the junction between crayfish lateral axons. By means of a glass capillary inserted into one of the axons, one side of the junction was perfused with solutions of known pH while the junctional resistance, Rj, was monitored. Integrity of the gap junction was checked electron microscopically. Rj remained unchanged when the pH of the perfusate was lowered from 7.1 to 6.0. However, when the pH of the unperfused side of the junction was lowered by substituting acetate for chloride in the external solution, Rj rose, attesting to the integrity of the junction and its capacity to uncouple in the perfused state. We suggest that H+ does not affect the junctional channels directly, but acts through an intermediary which is inactivated or removed by the perfusion.

Animals↗
PubMed1981

Electrotonic coupling in internally perfused crayfish segmented axons.

We have developed a technique for cannulation and internal perfusion of crayfish segmented lateral axons. Experiments on perfused and non-perfused axons lead to the following conclusions: 1. Internally perfused segmented axons behave very similarly to non-perfused axons. 2. The axial electrical resistance of the junctional region is almost as low as a comparable segment of axon. 3. Neither intracellular Ca2+ nor H+ is effective in disrupting the intercellular communication pathway in perfused axons. On the basis of these findings we have formulated a hypothesis for cellular control of intercellular coupling based on the existence of a soluble intermediate for Ca2+ or H+-induced uncoupling. This hypothesis is consistent with data from both internally perfused and non-perfused axons.

Animals↗
PubMed1980

Interaction of anaesthetics with electrical synapses.

Studies of the interaction of anaesthetics with various preparations, from whole animals to organic solvents, have been continuing since Overton and Meyer found a correlation between anaesthetic potency and solubility in olive oil. Although the physiological basis of anaesthesia is far from clear, one popular hypothesis is that anaesthetics act primarily by interfering with the normal functioning of chemical synapses. This hypothesis is supported by experiments showing that these synapses are more sensitive to both local and general anaesthetics than are axons. The effects of anaesthetics on electrical synapses (gap-junctions or nexus) have not previously been studied. These ubiquitous structures, presumably responsible for cell-to-cell communication, are found in most vertebrate and invertebrate tissues. We report here the effects of several anaesthetics on electronic coupling between nerve cells, and show that electrical synapses are less sensitive to most anaesthetics than are chemical synapses and axonal membranes.

Alcohols↗
PubMed1979

Propagation of action potentials in squid giant axons. Repetitive firing at regions of membrane inhomogeneities.

Effects of reduction in potassium conductance on impulse conduction were studied in squid giant axons. Internal perfusion of axons with tetraethylammonium (TEA) ions reduces G K and causes the duration of action potential to be increased up to 300 ms. This prolongation of action potentials does not change their conduction velocity. The shape of these propagating action potentials is similar to membrane action potentials in TEA. Axons with regions of differing membrane potassium conductances are obtained by perfusing the axon trunk and one of its two main branches with TEA after the second branch has been filled with normal perfusing solution. Although the latter is initially free of TEA, this ion diffuses in slowly. Up until a large amount of TEA has diffused into the second branch, action potentials in the two branches have very different durations. During this period, membrane regions with prolonged action potentials are a source of depolarizing current for the other, and repetitive activity may be initiated at transitional regions. After a single stimulus in either axon region, interactions between action potentials of different durations usually led to rebound, or a short burst, of action potentials. Complex interactions between two axon regions whose action potentials have different durations resembles electric activity recorded during some cardiac arrhythmias.

Action Potentials↗
PubMed1979

[Reference values of A.S.T., L.D.H., isoenzymes of L.D.H. and A.D.A. in cerebrospinal fluid of children (author's transl)].

From 230 C.S.F., authors found the reference values of A.S.T., L.D.H., isoenzymes of L.D.H. and A.D.A. in children from the area of Barcelona. The reference values obtained were: A.S.T.: n, 208; mean, 6.91 U/l., and s, +/- 2.71 U/l. A.D.A.: n, 175; percentil 50, 0.388 U/l.; percentil 97.5, 1.64 U/l., and percentil 2.5, 0 U/l. L.D.H.: n, 148; percentil 50, 9.54 U/l.; percentil 97.5, 24.96 U/l., and percentil 2.5, 3.81 U/l. Isoenzymes of L.D.H.: n, 82; L.D.H.-1: mean, 41.31 per cent and s, +/- 5.41 per cent. L.D.H.-2: mean, 30.79 per cent, and s, +/- 2.84 per cent. L.D.H.-3: mean, 20.3 per cent, and s, +/- 4.11 per cent. L.D.H.-4: mean, 6.02 per cent, and s, +/- 2.48 per cent. L.D.H.-5: mean, 2.47 per cent, and s, +/- 1.7 per cent. Higher activities of A.S.T. and L.D.H. were found in newborns, also varying the distribution of isoenzymes of L.D.H. The A.D.A didn't show variations.

Adenosine Deaminase↗
PubMed1978

Fine structure of the electrotonic synapse of the lateral giant axons in a crayfish (Procambarus clarkii).

The electrotonic synapse of lateral giant axons of the crayfish was studied by conventional thin sectioning. The most prominent membrane specialization observed in this synaptic region is the communicating junction. It is characterized by a close apposition of the two axonal membranes which are separated by a 4--5 nm wide gap. Other characteristics of the junction are an array of particles spaced about 20--22 nm apart and a row of vesicles symmetrically arranged at the cytoplasmic leaflets of each membrane. The communicating junction does not cover the entire surface of the electrotonic synapse. Indeed, we have found other specializations such as: finger-like Schwann cell processes extending between synaptic membranes, saccular invaginations of one synaptic membrane into its axon, and coated vesicles continuous with one of the membranes. In addition, large vesicular pieces of the communicating junctions, with their accompanying vesicles, appeared to extend deeply inside the axoplasm. The morphological appearance of the communicating junction is found to be different from the one reported for mammalian maculae communicans such as liver or heart muscle. This is surprising because, regardless of their morphological differences, both junctions seem to transmit electrotonically.

Animals↗
PubMed1978

Ephaptic transmission in squid giant axons.

Some characteristics of ephaptic transmission of action potentials were investigated with squid giant axons. For these studies two isolated axons were placed side by side or, on occasion, a single long axon was looped to form an "ephapse" between the axon trunk and one of its main branches. Extracellular potentials measured adjacent to axons surrounded by a very restricted volume of liquid ranged up to 80 mV in magnitude and had a shape similar to that of the membrane current. Intracellular records of the same axon regions show small voltage deflections; however, the transmembrane voltage (Vm = Vi - Vo) has the appearance of normally propagated action potentials. Ephaptic transmission of action potentials is possible when the ephaptic region is submerged in oil, as well as when the region is immersed in low-calcium solutions. When the speed of the propagated action potential is lowered by replacing the normal artifical seawater (ASW) with low-sodium ASW, some ephaptic effects are enhanced. It is concluded that in regions in which axons are confined by restricted extracellular volume, the large extracellular voltage changes arising during the passage of an action potential in one can cause ephaptic excitation in another.

Action Potentials↗
PubMed1976

Squid giant axons. A model for the neuron soma?

Insertion of electrically floating wires along the axis of a squid giant axon produces an apparent increase in diameter in the region where the wire surface has been treated to give it a low resistance. The shape of action potentials propagating into this region depend upon the surface resistance (and the length) of the wire. As this segment's internal resistance is lowered by reducing the wire's surface resistance, the following characteristic sequence of changes in the action potential is seen at the transition region: (a) the duration increases; (b) two peaks develop, the first one generated in the normal axon region and the second one generated later in the axial wire region, and; (c) blockage occurs (for a very low resistance wire). Action potentials recorded at the membrane region near the tip of the axial wire in (b) resemble those recorded at the initial segment of neurons upon antidromic invasions. Squid axon action potentials propagated from a normal region into that containing the low resistance wire also resemble antidromic invasions recorded in neuron somas. Hyperpolarizing current pulses applied through the wire act as if the wire surface resistance was momentarily reduced. For example, the two components of the action potential recorded at the axial wire membrane region noted in (b) can be sequentially blocked by the application of increasing hyperpolarizing current through the wire. Similar effects are seen when hyperpolarizing currents are injected into motoneuron somas. It is concluded that the geometrical properties of the junction of a neuron axon with its soma may be in themselves sufficient to determine the shape of the action potentials usually recorded by microelectrodes.

Action Potentials↗
PubMed1975

Axon voltage-clamp simulations. I. Methods and tests.

This is the first in a series of four papers in which we present the numerical simulation of the application of the voltage clamp technique to excitable cells. In this paper we describe the application of the Crank-Nicolson (1947) method for the solution of the parabolic partial differential equations that describe a cylindrical cell in which the ionic conductances are functions of voltage and time (Hodgkin and Huxley, 1952). This method is compared with other methods in terms of accuracy and speed of solution for a propagated action potential. In addition, differential equations representing a simple voltage-clamp electronic circuit are presented. Using the voltage clamp circuit equations, we simulate the voltage clamp of a single isopotential membrane patch and show how the parameters of the circuit affect the transient response of the patch to a step change in the control potential. The stimulation methods presented in this series of papers allow the evaluation of voltage clamp control of an excitable cell or a syncytium of excitable cells. To the extent that membrane parameters and geometrical factors can be determined, the methods presented here provide solutions for the voltage profile as a function of time.

Action Potentials↗