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Biomedical subjects

M M Goldner

Publications and source records attributed to M M Goldner.

8 recordsLinked to original sources
PubMed1979

Short-term effects of prednisolone on neuromuscular transmission in normal rats and those with experimental autoimmune myasthenia gravis.

Electrophysiological investigations of the effects of bath-applied prednisolone at the neuromuscular junction were performed in muscles from normal rats and rats with experimental autoimmune myasthenia gravis (EAMG). In muscles from both groups, prednisolone reversible and significantly depressed the amplitudes of minature end-plate potentials (MEPPs), end-plate potentials (EPPs) and indirectly elicited action potentials (APs) without affecting resting membrane potentials. Prednisolone also caused a significant reduction in EPP rise time to peak and half-decay time while markedly increasing MEPP frequency and AP rise time to peak and duration. These effects were shown to be dose-dependent. The percentage decrease in amplitude after prednisolone perfusion was similar for EPPs and MEPPs, indicating that the depressive effect of prednisolone at the junction is postsynaptic. In all of the parameters studied, the percentage effect of prednisolone was the same in EAMG and normal preparations. No stimulus-linked repetitive EPPs or APs were observed after prednisolone. It is concluded that prednisolone has a depressive effect on neuromuscular transmission, but that this occurs only at high concentrations of the drug which are not achieved during the treatment of myasthenia gravis.

Action Potentials↗
PubMed1977

Hyposmotic fluid formation in Hydra.

A detailed model for hyposmotic fluid formation in Hydra is presented. We propose that enteron fluid formation occurs in two steps: (1) segregation of an isosmotic fluid in large intercellular vacuoles with (2) subsequent reabsorption of solute in the intercellular channels to form the hyposmotic fluid of the enteron. Intercellular spaces in Hydra have been studied by light microscopy and thin-section electron microscopy, as well as by electrophysiological methods. These spaces are of two types: (1) large vacuoles which are located in the cells of both the epidermis and gastrodermis, being more numerous in the epidermis; and (2) lateral intercellular channels which run from the intercellular vacuoles, leading eventually to the enteron. These vacuoles and channels are highly convoluted, forming a complex three-dimensional network. We suggest that the network is involved in the water balance of Hydra.

Animals↗
PubMed1977

Effects of spin labeled acetylcholine analogs on cholinergic receptors of the leech.

The spin labeled acetylcholine analog, SL-2, which is a potent, non-stimulating muscarinic antagonist on the isolated frog heart, is a potent agonist a low concentrations (3x10-5 M) and an antagonist at slightly higher concentrations (4.5x10-5 M) on the mixed cholinergic receptors of the leech. Ion the other hand, the spin labeled acetylcholine analog, SL-1, possesses no agonist activity while it retains the antagonist activity of SL-2. Furthermore, the spin labeled analog, SL-3, which causes hyperpolarization and a decrease in action potential frequency, exhibits neither agonist nor antagonist activity.

Acetylcholine↗
PubMed1975

Voltage clamping with a single microelectrode.

A technique is described which allows neurons to be voltage clamped with a single microelectrode, and the advantages of this circuit with respect to conventional bridge techniques are discussed. In this circuit, the single microelectrode is rapidly switched from a current passing to a recording mode. The circuitry consists of: (1) an electronic switch; (2) a high impedance, ultralow input capacity amplifier; (3) a sample-and-hold module; (4) conventional voltage clamping circuitry. The closed electronic switch allows current to flow through the electrode. The switch then opens, and the electrode is in a recording mode. The low input capacity of the preamplifier allows the artifact from the current pulse to rapidly abate, after which time the circuit samples the membrane potential. This cycle is repeated at rates up to 10 kHz. The voltage clamping amplifier senses the output of the sample-and-hold module and adjusts the current pulse amplitude to maintain the desired membrane potential. The system was evaluated in Aplysia neurons by inserting two microelectrodes into a cell. One electrode was used to clamp the cell and the other to independently monitor membrane potential at a remote location in the soma.

Animals↗
PubMed1975

Dilantin-calcium interaction and active Na transport in frog skin.

The effects of diphenylhydantoin (DPH) and calcium were simultaneously studied on solute transport in frog skin. In the presence of external Ca, DPH elicited a significant increase in active Na transport; in its absence, DPH had no significant effect on active transport. DPH increased passive permeability, but this action was independent of Ca. It appears that the increase in active transport elicited by DPH is due to a specific interaction with Ca at the transport site.

Animals↗
PubMedDate not supplied

Facilitatory effects of 4-aminopyridine on normal neuromuscular transmission.

The effects of 4-aminopyridine (4-AP) on neuromuscular transmission were studied in vitro in the rat flexor digitorum longus muscles. 4-AP produced dose-dependent increases in endplate potential (EPP) amplitude, in rise time to peak, and in the average number of acetylcholine quanta released by presynaptic nerve impulses. The neuromuscular blocking effects of d-tubocurarine or low Ca2+/high Mg2+ concentrations could be completely reversed by 4-AP, and EPPs developed into muscle action potentials (APs). The drug had minimal effects on the amplitude or frequency of spontaneous miniature endplate potentials, but increased the duration of indirectly elicited muscle APs. The action of 4-AP required the presence of extracellular Ca2+; thus, its effect may be to promote Ca2+ entry into the motor nerve terminal, and thereby increase the neurally evoked transmitter release. 4-AP is effective in overcoming both presynaptic and postsynaptic blockade of neuromuscular transmission, suggesting a potential role for this drug in the treatment of neuromuscular diseases.

Aminopyridines↗
PubMedDate not supplied

Facilitatory effects of 4-aminopyridine on neuromuscular transmission in disease states.

The in vitro effects of 4-aminopyridine (4-AP) on neuromuscular transmission were determined by microelectrode techniques in intercostal muscles from patients with myasthenia gravis (MG) and the Eaton-Lambert syndrome (ELS), and in forelimb muscles from rats with experimental autoimmune myasthenia gravis (EAMG). In MG and EAMG, the amplitudes of miniature endplate potentials (MEPPs) and endplate potentials (EPPs) were reduced, and there was increased sensitivity to the blocking action of d-tubocurarine (dTc). In ELS, MEPP amplitude was normal but the average number of acetylcholine quanta released by nerve impulses was reduced, causing subthreshold EPPs. In EAMG muscle, 4-AP produced dose-dependent increases in EPP amplitude and in the duration of indirectly elicited muscle action potentials but no changes in MEPP amplitude and resting membrane potential. 4-AP completely reversed the postsynaptic blockade produced by dTc and EAMG. 4-AP appears to facilitate neuromuscular transmission in EAMG, MG, and ELS by increasing the neurally evoked transmitter release, thus overcoming either the pre- or the postsynaptic neuromuscular blockade.

Adult↗