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H GRUNDFEST

Publications and source records attributed to H GRUNDFEST.

At least 19 recordsLinked to original sources
PubMed1964

EEL ELECTROPLAQUES: SPIKE ELECTROGENESIS WITHOUT POTASSIUM ACTIVATION.

Measurements with the voltage clamp technique demonstrate that only an early conductance increase occurs during spike electrogenesis of eel electroplaques. The delayed increase which is characteristic of spike electrogenesis in many other cells is absent. Instead, the membrane resistance increases two- to threefold above its resting value. The brief initial increase in conductance is due to sodium activation followed by rapid sodium inactivation. The influx of sodium causes an inward current of up to 80 ma/cm2. The inward current is abolished by eliminating the sodium from the normal medium (substitution of choline chloride for NaCl); by blocking sodium activation with tetrodotoxin; or by causing sodium inactivation through enrichment of the potassium in the medium. The delayed increase in membrane resistance is not affected by eliminating sodium influx, nor by substituting various impermeable anions for the chlorine of the normal medium. Thus, the increase in resistance signifies the occurrence of potassium inactivation which is unmasked by the absence of potassium activation.

Animals↗
PubMed1964

INHIBITORY POSTSYNAPTIC POTENTIALS IN GRASSHOPPER MUSCLE.

Hyperpolarizing inhibitory postsynaptic potentials have been discovered in fibers of the "jumping" muscle of the grasshopper. These potentials attenuate the depolarizing excitatory postsynaptic responses. They are enhanced during depolarization of the muscle fiber with applied current and are diminished and then reversed during hyperpolarization. The electrogenesisappears to be caused by chloride-activation. Gamma-aminobutyric acid activates the inhibitorysynaptic membrane and picrotoxin is an inactivator agent.

Animals↗
PubMed1964

WATER TRANSFER AND CELL STRUCTURE IN ISOLATED CRAYFISH MUSCLE FIBERS.

Changes in volume of crayfish single muscle fibers in response to changes in ionic or electrical conditions have been studied in conjunction with electrophysiological measurements and electron microscopic examinations. The occurrence of at least three mechanisms of water movements is revealed, two being processes which are superimposed on the normal osmotic water movement that results from a change in the concentration of solute in the medium. Differences between the time courses of the changes in volume and potential on changing K(i)/K(o) indicate that water may be distributed unequally for a time within compartments of the fiber. Electron micrographs reveal a selective accumulation of water at the periphery of the fiber under certain conditions. A correlation of H(2)O transfer with a change in membrane potential is apparent in crayfish muscle fibers and is probably due to electroosmotic effects. Electrokinetic water movements are produced whenever the membrane potential is changed to a considerable degree by changing the level of K and/or Cl in the medium, or by applying currents with an intracellular microelectrode. Depolarizations cause shrinkage. Hyperpolarizations or repolarizations cause swelling. The volume changes are independent of the occurrence or absence of swelling in the anion-permselective transverse tubular system. They indicate that the fiber membrane along the surface is heterogeneous, not only with respect to the signs of its fixed charge sites, but also with respect to the sizes and relative permselectivities of these charged channels.

Animals↗
PubMed1963

MUSCLE: VOLUME CHANGES IN ISOLATED SINGLE FIBERS.

Volumetric experiments on single fibers isolated from semiten-dinosus muscles of frogs, some performed in correlation with measurements of membrane potential, confirm the data obtained on whole muscles, but only for the specific range of conditions in which most of the latter experiments have been done. These conditions are restricted to media in which the anion ( Cl usually) is permanent and the K is 10 to 12.5 meqlliter, or four to five times above the normal level in Ringer's solution. When other ionic conditions are employed, phenomena are disclosed which have not previously been described. The findings throw doubt upon the validity of some generally accepted views regarding the permeability properties of the membrane of frog muscle fibers and regarding the nature of the mechanisms which regulate their volume.

Animals↗
PubMed1963

EVIDENCE FOR ANION-PERMSELECTIVE MEMBRANE IN CRAYFISH MUSCLE FIBERS AND ITS POSSIBLE ROLE IN EXCITATION-CONTRACTION COUPLING.

Under certain conditions only, isolated crayfish skeletal muscle fibers change in appearance, becoming grainy, darkening, and seemingly losing their striations. These changes result from development of large vesicles on both sides of the Z-line. The longitudinal sarcoplasmic reticulum remains unaffected. The vesicles are due to swelling of a transverse tubular system (TTS) which is presumably homologous with the T-system tubules of other muscle fibers. The vesiculations occur during efflux of water or on reducing external K or Cl, but only when KCl can leave the fiber. They never result from osmotic, ionic, or electrical changes when KCl cannot leave. Inward currents, applied through a KCl-filled intracellular cathode, also cause the vesiculations. These are not produced when the cathode is filled with K-propionate, nor by outward or longitudinal currents. Thus the transverse tubules swell only when Cl leaves the cell. Accordingly, their membrane is largely or exclusively anion-permselective. These findings also indicate that the TTS forms part of a current loop, connecting with the exterior of the fiber probably through radial tubules (RT) possessing membrane of low conductivity. Thus, part of the current flowing inward across the sarcolemma during activity can return to the exterior through the membrane of the TTS. The structure and properties of the latter offer the possibility for an efficient electrical mechanism to initiate excitation-contraction coupling.

Animals↗
PubMed1961

Electron microscopic and histochemical comparison of the two types of electroplaques of Narcine brasiliensis.

The torpedine electric fish Narcine brasiliensis has two morphologically distinct electric organs (main and accessory) which also differ with respect to a number of electrophysiological properties. The fine structure of the electroplaques of these organs has been examined by electron microscopy and by a histochemical method for localizing esterase activity with a high degree of resolution. In both kinds of electroplaques the innervated surface (ventral in those of the main organ, dorsal in those of the accessory) is the only site of esterase activity. The latter is further confined to the regions of synaptic contact between vesicle-containing axon terminals and the electroplaque membrane. The synaptic apparatus is similar to, but less elaborate than, that of neuromuscular junctions. The axon terminals and electroplaque membranes are free of connective tissue envelopments. The membrane of the uninnervated surfaces forms a continuum with a dense canalicular network which penetrates deeply into the 7 micro thick electroplaques of the main organ. The canalicular network has about the same thickness in the 20 micro electroplaques of the accessory organ. Except for this difference, the two kinds of cells appear to have the same fine structure. This finding is discussed in relation to the electrophysiological data on functional differences.

Animals↗
PubMed1961

Graded and all-or-none electrogenesis in arthropod muscle. I. The effects of alkali-earth cations on the neuromuscular system of Romalea microptera.

Graded electrically excited responsiveness of Romalea muscle fibers is converted to all-or-none activity by Ba(++), Sr(++), or Ca(++), the two former being much the more effective in this action. The change occurs with as little as 7 to 10 per cent of Na(+) substituted by Ba(++). The spikes now produced have overshoots and may be extremely prolonged, lasting many seconds. During the spike the membrane resistance is lower than in the resting fiber, but the resting resistance and time constant are considerably increased by the alkali-earth ions. The excitability is also increased, spikes arising neurogenically from spontaneous repetitive discharges in the axon as well as myogenically from spontaneous activity in the muscle fibers. Repetitive responses frequently occur on intracellular stimulation with a brief pulse. The data indicate that the alkali-earth ions exert a complex of effects on the different action components of electrically excitable membrane. They may be described in terms of the ionic theory as follows: The resting K(+) conductance is diminished. The sodium inactivation process is also diminished, and sodium activation may be increased. Together these changes can act to convert graded responsiveness to the all-or-none variety. The alkali-earth ions can also to some degree carry inward positive charge during activity, since spikes are produced when Na(+) is fully replaced with the divalent ions.

Alkalies↗
PubMed1961

Graded and all-or-none electrogenesis in arthropod muscle. II. The effects of alkali-earth and onium ions on lobster muscle fibers.

Conversion of graded responsiveness of lobster muscle fibers to all-or-none activity by alkali-earth and tetraethylammonium (TEA) ions appears to be due to a combination of effects. The membrane is hyperpolarized, its resistance is increased, and its sensitivity to external K(+) is diminished, all effects which indicate diminished K(+) conductance. While the spikes are prolonged, the conductance is higher throughout the response than it is in the resting membrane. Repetitive activity becomes prominent. These effects indicate maintained high conductance for an ion which causes depolarization. This is normally Na(+), since its presence in low concentrations potentiates the effects of Ba(++), but the alkali-earth ions and TEA can also carry inward charge. Ba(++), Sr(++), and TEA appear to be more effective than is Ca(++) in its normal role, which is probably to depress K(+) conductance and Na inactivation. Thus, conversion of graded to all-or-none responsiveness appears to occur because of the relative increase of depolarizing inward ion flux and decrease of repolarizing outward flux.

Alkalies↗