Chloride current induced by injection of calcium into Xenopus oocytes.

Membrane currents of Xenopus oocytes were studied with the membrane under voltage clamp. Intracellular injection of the calcium-chelating agent EGTA reduced, or abolished, the transient outward chloride current normally activated by membrane depolarization. Intracellular injection of calcium ions evoked large membrane currents, which inverted direction close to the chloride equilibrium potential.

Separate fractions of mRNA from Torpedo electric organ induce chloride channels and acetylcholine receptors in Xenopus oocytes.

Poly(A)+ mRNA extracted from the electric organ of Torpedo was fractionated by sucrose density gradient centrifugation. After injection into Xenopus oocytes one mRNA fraction induced the appearance of chloride channels in the oocyte membrane. Many of these channels were normally open, and the ensuing chloride current kept the resting potential of injected oocytes close to the chloride equilibrium potential.

Slowly inactivating potassium channels induced in Xenopus oocytes by messenger ribonucleic acid from Torpedo brain.

Poly(A+) messenger RNA was extracted from the electric lobe and medulla of Torpedo and injected into oocytes of Xenopus laevis. The synthesis and processing of proteins coded by the injected messenger RNA led to the incorporation of voltage-activated channels in the oocyte membrane. A large, well maintained outward current was recorded from injected oocytes in response to depolarization.

Extracellular ions and excitation-contraction coupling in frog twitch muscle fibres.

Intracellular calcium transients were recorded from voltage-clamped frog twitch muscle fibres using Arsenazo III. The possible role of extracellular ions in excitation-contraction (e.-c.

A study of the submaxillaris muscle of the frog.

The characteristics of muscle fibres in the submaxillaris muscle of the frog were studied using electrophysiological and anatomical techniques. The muscle fibres were capable of eliciting action potentials and their passive membrane properties were similar to those of fast muscle fibres. Composite end-plate potentials, due to polyneuronal innervation, were observed in most muscle fibres.

Characteristics of membrane channels induced by acetylcholine at frog muscle-tendon junctions.

The membrane at the tendinous ends of frog muscle fibres has acetylcholine (ACh) receptors that are blocked by alpha-bungarotoxin. The properties of ACh-activated channels in the myotendinous region were investigated by noise analysis. These channels displayed the same characteristics in normal, denervated and reinnervated muscles.

Properties of human brain glycine receptors expressed in Xenopus oocytes.

Glycine and gamma-aminobutyric acid (GABA) receptors from the foetal human brain were 'transplanted' into the Xenopus oocyte membrane by injecting the oocytes with poly(A)+-mRNA extracted from the cerebral cortex. Activation of both glycine and GABA receptors induced membrane currents carried largely by chloride ions. However, unlike the GABA-activated current, the glycine current was blocked by strychnine, and was not potentiated by barbiturate.

Glutamate and kainate receptors induced by rat brain messenger RNA in Xenopus oocytes.

Xenopus laevis oocytes injected with poly(A)+ mRNA extracted from rat brain became sensitive to serotonin, glutamate, kainate, acetylcholine and gamma-aminobutyrate. Application of these substances to mRNA-injected oocytes elicited membrane currents. The glutamate- and acetylcholine-induced currents usually showed oscillations, while the kainate current was smooth.

Acetylcholinesterase activity in intact and homogenized skeletal muscle of the frog.

Enzymatic hydrolysis of acetylcholine (ACh) was determined in intact frog sartorius muscles or their homogenates. The Vmax was 29 nmol min-1 in intact muscles and 46 nmol min-1 per muscle in homogenates, and the Km was 6 and 0.2 mM, respectively.

Messenger RNA from human brain induces drug- and voltage-operated channels in Xenopus oocytes.

Sodium channels and receptors to serotonin and kainate were 'transplanted' from human brain into frog oocytes, by isolating messenger RNA from a fetal brain, and injecting it into Xenopus laevis oocytes. The mRNA was translated by the oocyte and induced the appearance of functional receptors and channels in its membrane. This approach renders drug- and voltage-operated channels of the human brain more amenable to detailed study.

Electrophysiological and neurochemical investigations of the action of presynaptic neurotoxins.

Previous experiments have suggested that hemicholinium-3 might directly antagonize certain actions of beta-bungarotoxin at the neuromuscular junction. Data presented here show that, on the contrary, hemicholinium-3 neither inhibits the phospholipase activity of beta-bungarotoxin nor does it affect the characteristic pattern of transmitter release observed at end plates exposed to the toxin. Lanthanum ions were found to promote the release of acetylcholine from sartorius nerve-muscle preparations that had been paralyzed by botulinum toxin.

Acetylcholinesterase activity of Xenopus laevis oocytes.

The cholinesterase activity of Xenopus laevis oocytes was assessed using [3H]acetylcholine in a simple radiometric procedure. The cholinesterase activity of mature (stage V-Vl) oocytes was very sensitive to inhibition by the specific acetylcholinesterase inhibitor, BW284-C5l, and relatively insensitive to an inhibitor of non-specific, or butyrylcholinesterase. The Km and Vmax of the acetylcholinesterase measured in homogenates of oocytes were 312 microM and 4.

Voltage-operated channels induced by foreign messenger RNA in Xenopus oocytes.

Poly(A)+ messenger RNA (mRNA) extracted from rat brains or from cat muscles was injected into Xenopus laevis oocytes. This led to the incorporation of voltage-operated Na+ and K+ channels into the oocyte membrane. These channels are not normally present in the oocyte and presumably result from the synthesis and processing of proteins coded by the injected mRNA.

Changes in threshold for calcium transients in frog skeletal muscle fibres owing to calcium depletion in the T-tubules.

Strength-duration curves were measured for voltage-clamp depolarizations required to elicit a just detectable rise in intracellular calcium, as monitored using arsenazo III, in frog twitch muscle fibres. In normal Ringer solution, the threshold for a 5 sec duration depolarization was about 5 mV more negative than for a 200 msec duration pulse. The shift in threshold comparing 200 msec and 5 sec pulses was almost abolished in bathing solutions including magnesium or nickel (4 mM), or where the free calcium concentration was buffered.

Divalent cations and temperature dependent block of impulse propagation at the frog neuromuscular junction.

End-plate potentials were recorded from superficial muscle fibers of the frog sartorius nerve-muscle preparation. Exposure of the preparation to a medium containing a high divalent cation concentration, produced a temperature dependent failure of neuromuscular transmission. Failure of transmission developed in an "all-or-none" mode and was reversed by decreasing the bath temperature or divalent cation concentration.

Morphological and physiological changes in dissociated adult frog muscle fibres after prolonged culturing.

Adult frog (Rana temporaria) muscle fibres, denervated in vivo, were dissociated and maintained in culture for several weeks. Light and electron microscopical studies showed that the fibres developed striated muscle sprouts. These sprouts were in cytoplasmic continuity with the parent muscle fibre.

Serotonin receptors induced by exogenous messenger RNA in Xenopus oocytes.

When poly(A)+-mRNA, extracted from rat brain, was injected into Xenopus laevis oocytes, it induced the appearance of serotonin receptors in the oocyte membrane. Application of serotonin to injected oocytes elicited, after a long delay, oscillations in membrane current. The equilibrium potential of this current corresponded with the chloride equilibrium potential.

Recording of single gamma-aminobutyrate- and acetylcholine-activated receptor channels translated by exogenous mRNA in Xenopus oocytes.

High resolution ('giga-seal') patch clamp recording in Xenopus oocytes was used to measure single channel currents from ACh- and GABA-activated receptors. The proteins that make up these receptors had been translated from mRNA derived from, respectively, denervated cat muscle and chick optic lobe.

Aequorin-calcium transients in frog twitch muscle fibres.

Intracellular Ca2+ transients, evoked either by action potentials or depolarizing clamp pulses, were studied in frog sartorius muscle fibres injected with aequorin. The time course of the Ca2+ transients became shorter as the temperature was increased. The half rise time and decay time constants showed straight lines between 3 and 30 degrees C in Arrhenius plots, with a Q10 of 2.

Calcium transients studied under voltage-clamp control in frog twitch muscle fibres.

1. Intracellular calcium transients were recorded from frog twitch muscle fibres in response to voltage-clamped depolarizing pulses, using arsenazo III as an intracellular calcium monitor. The object was to investigate the time- and voltage-dependent characteristics of the coupling process between membrane depolarization and calcium release from the sarcoplasmic reticulum (s.

Calcium transients in frog skeletal muscle fibres following conditioning stimuli.

1. Intracellular Ca(2+) transients were recorded from frog twitch muscle fibres, using arsenazo III as a Ca(2+) monitor. When fibres were stimulated by two action potentials, the arsenazo signal to the second stimulus was smaller than the first, for stimulus intervals of up to several seconds.

Block of glutamate-activated synaptic channels by curare and gallamine.

Excitatory junctional currents (e.j.cs) and glutamate-activated currents have been examined in voltage-clamped locust muscle fibres exposed to curare or gallamine.

Electrophysiological and chemical determination of acetylcholine release at the frog neuromuscular junction.

1. Mass fragmentography was used to measure the tissue content and release of acetylcholine (ACh) by frog sartorius muscles, which had been previously treated with an irreversible cholinesterase inhibitor. The frequency of miniature end-plate currents (m.

Denervation changes in normal and myasthenia gravis human muscle fibres during organ culture.

1. Human intercostal nerve-muscle obtained from normal and myasthenia gravis affected patients has been organ cultured for up to 5 weeks at 23 degrees C. In addition normal nerve-muscle has been cultured for up to 2 weeks at 36 degrees C.

Calcium transients evoked by action potentials in frog twitch muscle fibres.

1. Intracellular Ca(2+) transients were recorded from frog twitch muscle fibres in response to action potentials and repetitive stimulation, using ionophoretically injected arsenazo III as a Ca(2+) monitor. A dual wave-length optical system was used to measure absorbance changes of the injected dye from small areas of single fibres within the cutaneous pectoris muscle.