Lobster muscle and synapse respond to cortisol, a vertebrate hormone

1983 ◽  
Vol 61 (8) ◽  
pp. 836-840 ◽  
Author(s):  
D. Dixon ◽  
H. L. Atwood
Keyword(s):  
Membrane Potential ◽  
Neuromuscular Transmission ◽  
Physiological Role ◽  
Homarus Americanus ◽  
Membrane Resistance ◽  
Rapid Onset ◽  
Excitatory Postsynaptic Potentials ◽  
Fiber Membrane ◽  
Postsynaptic Potentials ◽  
Muscle Fiber Membrane

Cortisol (0.28 μmol∙L−1) applied to lobster (Homarus americanus) neuromuscular preparations produces a hyper-polarization in muscle fibers and an increase in amplitude of excitatory postsynaptic potentials. The effect appears to be surface-mediated, because of its rapid onset (within seconds). It is also Na+–K+ ATPase dependent, because ouabain blocks the effects. The effects are relatively short-lasting, and gradually subside within 15 min. The increase in excitatory postsynaptic potentials is attributed in part to increased quantal output of transmitter, and not to changes in muscle fiber membrane resistance. The effects of cortisol on neuromuscular transmission and membrane potential indicate that cortisol may have a physiological role in crustaceans.

Influence of nitrate and other anions on fast and slow contractions of crab muscle

1968 ◽  
Vol 46 (1) ◽  
pp. 1-9 ◽  
Author(s):  
H. L. Atwood
Keyword(s):  
Membrane Potential ◽  
Muscle Fiber ◽  
Membrane Resistance ◽  
Single Muscle ◽  
Fiber Membrane ◽  
Tension Development ◽  
Muscle Fiber Membrane ◽  
Slow Contraction ◽  
Potential Threshold ◽  
Bathing Fluid

The effects of bromide, nitrate, iodide, and thiocyanate ions on the neurally evoked fast and slow contractions of a crab muscle were investigated. Both types of contraction were depressed in bromide and nitrate. In iodide and thiocyanate, the slow contraction was often depressed but the fast contraction was potentiated. The foreign anions increased muscle fiber membrane resistance and the amplitudes of both fast and slow postsynaptic potentials. Records of tension development in single muscle fibers showed that more stimulating current was required to produce a given tension in nitrate than in the standard bathing fluid; this change was related to hyperpolarization of the muscle fiber membrane in nitrate. Potassium contractures also were inhibited by nitrate, because of the less effective depolarization of the cell membrane by potassium ion in the presence of nitrate. No marked shift in the membrane potential threshold for contraction occurred after treatment with the foreign anions.

Stabilization and rectification of muscle fiber membrane by tetrodotoxin

1960 ◽  
Vol 198 (5) ◽  
pp. 934-938 ◽  
Author(s):  
Toshio Narahashi ◽  
Takehiko Deguchi ◽  
Norimoto Urakawa ◽  
Yoshio Ohkubo
Keyword(s):  
Muscle Fiber ◽  
Muscle Fibers ◽  
Membrane Resistance ◽  
Frog Muscle ◽  
Resting Potential ◽  
Fiber Membrane ◽  
Delayed Rectification ◽  
Intracellular Microelectrodes ◽  
Cathodal Current ◽  
Muscle Fiber Membrane

The mode of action of tetrodotoxin on the frog muscle fiber membrane has been analyzed with the aid of intracellular microelectrodes. Tetrodotoxin of 10–7 concentration made the applied cathodal current ineffective in producing action potential, whereas the resting potential and resting membrane resistance underwent little or no change. With 10–8 tetrodotoxin the muscle fibers responded with the small action potentials at high critical depolarizations. These results can be explained on the basis of the membrane being stabilized by inactivation of the sodium-carrying mechanism. Although delayed rectification was not observed in normal muscle fibers, it became apparent in the fibers rendered inexcitable by tetrodotoxin. This finding, together with other evidence in the existing literature, supports an applicability of the sodium theory to the frog muscle fibers.

scholarly journals Permeability of Alkali Metal Cations in Lobster Muscle

1968 ◽  
Vol 51 (3) ◽  
pp. 399-425 ◽  
Author(s):  
Harold Gainer ◽  
Harry Grundfest
Keyword(s):  
Membrane Potential ◽  
Muscle Fiber ◽  
Single Muscle ◽  
Alkali Metal Cations ◽  
Fiber Membrane ◽  
Osmotic Permeability ◽  
Hyperosmotic Condition ◽  
Time Courses ◽  
Muscle Fiber Membrane ◽  
External K

Single muscle fibers from lobster walking legs are effectively impermeable to Na, but are permeable to K. They shrink in hyperosmotic NaCl; they swell in low NaCl media which are hyposmotic or which are made isosmotic with the addition of KCl. In conformity, the membrane potential is relatively insensitive to changes in external Na, while it responds according to the Nernst relation for changes in external K. When the medium is made isosmotic or hyperosmotic with RbCl the volume and membrane potential changes are of essentially the same magnitudes as those in media enriched with KCl. The time courses for attaining equilibrium are slower, indicating that Rb is less permeant than K. Substitution of CsCl for NaCl (isosmotic condition) produces no change in volume of the muscle fiber. Addition of CsCl (hyperosmotic condition) causes a shrinkage which attains a steady state, as is the case in hyperosmotic NaCl. Osmotically, therefore, Cs appears to be no more permeant than is Na. However, the membrane depolarizes slowly in Cs-enriched media and eventually comes to behave as an ideal Cs electrode. Thus, the electrode properties of the lobster muscle fiber membrane may not depend upon the diffusional relations of the membrane and ions, and the osmotic permeability of the membrane for a given cation may not correspond with the electrophysiologically deduced permeability. Comparative data on the effects of NH4 and Li are also included and indicate several other degrees of complexity in the cell membrane.

Effects of the inflammatory mediator prostaglandin E2 on myenteric neurons in guinea pig ileum

1997 ◽  
Vol 272 (6) ◽  
pp. G1451-G1456 ◽  
Author(s):  
J. A. Dekkers ◽  
L. M. Akkermans ◽  
A. B. Kroese
Keyword(s):  
Prostaglandin E2 ◽  
Myenteric Plexus ◽  
Inflammatory Mediator ◽  
Direct Action ◽  
Membrane Resistance ◽  
Excitatory Postsynaptic Potentials ◽  
Postsynaptic Potentials ◽  
Myenteric Neurons ◽  
Bath Application ◽  
Slow Depolarization

The effects of the inflammatory mediator prostaglandin E2 (PGE2) on myenteric neurons were investigated by intracellular recordings in a conventional plexus preparation. Bath application of PGE2 (1-1,000 nM) evoked a concentration-dependent and reversible slow depolarization and an augmentation of excitability in 23 of 26 AH and 12 of 13 S neurons. The amplitude of the slow depolarization ranged from 4 +/- 1 mV at 1 nM to 13 +/- 3 mV at 1 microM in S and AH neurons. In AH neurons, PGE2 evoked an increase in membrane resistance and a reduction of afterhyperpolarization. In S neurons, PGE2 evoked either an increase or a decrease in membrane resistance. PGE2 slightly reduced the amplitude of electrically evoked fast excitatory postsynaptic potentials and had no effect on slow excitatory postsynaptic potentials. Moreover, PGE2 evoked bursts of fast excitatory postsynaptic potentials and action potentials in S neurons, indicative of cyclical neural activity in the myenteric plexus. It is concluded that the inflammatory mediator PGE2 can act as an excitatory neuromodulator of gastrointestinal motility through direct action on neurons in the myenteric plexus.

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