Slowing of the time course of the excitation of squid giant axons in viscous solutions

Kukita, Fumio; Yamagishi, Shunichi

doi:10.1007/bf01869083

Cited by 14 publications

(24 citation statements)

References 24 publications

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“…The rising and falling phases of the action potential were affected to the same extent, so that the amplitude of action potential did not change. As shown elsewhere (KUKITA and YAMAGISHI, 1979), both inward and outward currents measured under voltage clamp conditions decreased and were slowed down to the same extent in hypertonic solutions. These effects on the time course were not specific for any special channel but were similar to the effects of changing temperature (HODGKIN and KATZ, 1949b).…”

Section: Discussionsupporting

confidence: 80%

Excitation of Squid Giant Axons in Hypotonic and Hypertonic Solutions

Kukita

Yamagishi

1979

Jpn.J.Physiol

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Excitability of intracellularly perfused squid giant axons was maintained in hypotonic solutions (down to 300 mOSM) and in hypertonic solutions (up to about 10 OSM), when osmolalities of internal and external solutions were adjusted to be equal with glycerol, glucose, or sucrose. Molar concentrations of ions were kept constant during one series of experiments. The resting potential and the amplitude of the action potential did not change in both hypotonic and hypertonic solutions. With reduction of osmolality, the duration of action potential decreased and the maximum rate of rise and conduction velocity increased. By raising osmolality, the duration was prolonged and the maximum rate of rise and the conduction velocity decreased. Effects of osmolality change were almost reversible. However, these effects were not directly related to the osmolality change but seemed to be related to the viscosity change of the solutions. When the osmolality of external solution was raised with NaCl (up to 2.6 M NaCl), the overshoot increased in proportion to the logarithm of the NaCl concentration. The slope of increase was about 50 mV/decade. However, the resting potential showed little change. With increase of the NaCl concentration, the duration of the action potential increased.Physiological experiment with nerves are usually performed in isotonic solutions. An osmolality change in bathing solutions around intact nerves is thought to have some effect on nerves, mainly due to an inflow or an outflow of water across the membrane accompanied with a volume change of cells. Use of isotonic solutions alone limits the range of ionic concentration changes that can be made. Until now, many investigators have examined the excitability of nerves (MULLER-MOHNSSEN and BARSKE, 1974) or muscle (HODGKIN and HOROWICZ, 1957;KAWATA et al., 1974;SUAREZ-KURTZ and SORENSON, 1977) in hypotonic and hypertonic solutions. Since they used intact cells, it was difficult to separate the effect of the intended ionic concentration changes from those of changes in cell volume, in cell surface area and in ionic concentrations inside the cell (FREEMAN et al., 1966;

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Section: Discussionsupporting

confidence: 80%

Excitation of Squid Giant Axons in Hypotonic and Hypertonic Solutions

Kukita

Yamagishi

1979

Jpn.J.Physiol

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“…When the internal potassium concentration was lower or TTX was applied to the external solution, the shift was also observed and tended to be smaller by a few inV. When the osmolities on both sides of the membrane were raised under the condition that there was no water flow, the properties of the membrane currents did not change essentially (Kukita & Yamagishi, 1979). Under this condition, the same osmotic gradient effect can be observed when 1 M urea was added to the hypertonic external solution.…”

Section: Membrane Currents Under the Outward Water Flowsupporting

confidence: 69%

“…Instead of ions, nonelectrolyte molecules can be used to analyze the structure of the other part of the ionic channel, because they by themselves do not carry electrical charges and only affect the movement of ions by altering the microscopic viscosity around ions and/or producing the hydrodynamic flow of water. The effects of the microscopic viscosity on the nerve excitation was reported previously (Kukita & Yamagishi, 1979). In this report, we describe the effects of the outward water flow through the membrane on action potentials and ionic currents during the nerve excitation.…”

Section: Introductionmentioning

confidence: 81%

“…1 showed that the main cause of increasing the undershoot was the outward water flow but not the specific effects of any molecules. The duration of the action potential increased when the water flow was stopped, because a slowing down effect by a viscosity increase was clearly observed in the action potential only under the condition of no water flow (Kukita & Yamagishi, 1979).…”

Section: Action Potentials Under the Outward Water Flowmentioning

confidence: 98%

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Effects of an outward water flow on potassium currents in a squid giant axon

Kukita

Yamagishi

1983

J. Membrain Biol.

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The excitation of the squid giant axon was analyzed under an outward water flow through the membrane product by an osmotic gradient. The outward water flow made an undershoot of the action potential larger by about 25 mV without decreasing its peak largely. It also made EK more negative but not ENa. The effect of the outward water flow was specific for the potassium channel. The outward current increased and its decline during a long-lasting depolarization became less prominent under the outward water flow. At the same time, inward tail currents for the potassium channel decreased extraordinarily without a large change in the time course. The potassium conductance had a marked rectification in the direction of the water flow. The undershoot of the action potential under the outward water flow was very sensitive to potassium ions in the external solution. Eight mM KCl was effective to diminish the undershoot and to restore the change in EK by about 60% but gave no effect on the reduced tail current. The outward water flow effect can be explained not only by the change in a local concentration of potassium ions at the mouths of the potassium channel due to a sieving but also by the rectification in a hydrodynamic manner.

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“…amplitude in low sodium solutions is increased by slower channel kinetics, with resultant longer-lasting synaptic current, or that transmitter re-uptake is slowed (Crawford & McBurney, 1977). Changes in time course of synaptic current could be brought about by altered viscosity of the low sodium solution (Kukita & Yamagishi, 1979;Nelson, Anholt, Lindstrom & Montal, 1980;Shikoumas, French, Belamarich, Brodwick & Eaton, 1981) in low sodium (LS), in monensin plus low sodium (M, LS; averages for three 3 min periods), in monensin plus normal sodium (M, NS; averages for three 3 min periods), and during washout (NS; averages for four 3 minute periods). Since all e.p.s.p.s initially larger than 1 mV increased in low sodium, experiments to test the effect of changing external sodium concentration on the response to monensin were conducted with this type of fibre exclusively.…”

Section: Resultsmentioning

confidence: 99%

Neuromuscular transmission in crustaceans is enhanced by a sodium ionophore, monensin, and by prolonged stimulation.

Atwood¹,

Charlton²,

Thompson³

1983

The Journal of Physiology

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SUMMARY1. A sodium ionophore, monensin, was applied to crustacean neuromuscular preparations to determine whether increased intracellular sodium could lead to enhancement of transmitter release similar to that observed with prolonged stimulation.2. Following a single application of monensin (3-13 ItM), the excitatory postsynaptic potential (e.p.s.p.) increased in amplitude by 50-800%. The increase was entirely due to a presynaptic effect that resulted in higher quantal content of transmission and increased frequency of spontaneous miniature potentials. A second application of monensin was less effective than the first.3. Application of monensin in calcium-free solutions led to rapid, marked enhancement of the e.p.s.p. upon restoration of the normal physiological solution, indicating that monensin can produce its effects in the absence of external calcium. Spontaneous miniature potentials often occurred more frequently in calcium-free solution after monensin had been applied.4. The extent of enhancement of e.p.s.p. amplitude depended on the concentration of external sodium, being smaller in solutions of low sodium.5. Prolonged stimulation of the motor axon usually enhanced the e.p.s.p. to a greater extent than application of monensin alone, but the time course of recovery of e.p.s.p. amplitude was similar in both cases.6. We conclude that the increase in e.p.s.p. amplitude promoted by monensin can be attributed to increased transmitter output resulting from influx of sodium into the nerve terminal. Increased intracellular sodium may lead to a rise in intracellular calcium ion concentration.7. Some features of long-term facilitation of transmitter release can be attributed to build-up of intracellular sodium during stimulation.

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Slowing of the time course of the excitation of squid giant axons in viscous solutions

Cited by 14 publications

References 24 publications

Excitation of Squid Giant Axons in Hypotonic and Hypertonic Solutions

Excitation of Squid Giant Axons in Hypotonic and Hypertonic Solutions

Effects of an outward water flow on potassium currents in a squid giant axon

Neuromuscular transmission in crustaceans is enhanced by a sodium ionophore, monensin, and by prolonged stimulation.

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