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R T Kado

Publications and source records attributed to R T Kado.

At least 37 records · Page 2Linked to original sources
PubMed1987

Voltage-clamp analysis of a crayfish rectifying synapse.

1. The rectifying crayfish giant motor synapse has been studied in the second abdominal ganglion, using the double-voltage-clamp technique which allowed direct measurements of junctional current at various fixed transjunctional potentials. 2. The transjunctional potential (Vj), defined as the difference between the voltages recorded in the lateral giant axon and the giant motor fibre, was varied from -70 to +50 mV, the minimum and maximum junctional chord conductances (gmin and gmax, respectively) were found to be 1.2 +/- 1.3 microS (n = 10) and 22.9 +/- 6.3 microS (n = 10), respectively. 3. For a given Vj, changes in the lateral giant axon or giant motor fibre membrane potential over a range of +/- 30 mV around their resting levels did not influence the junctional permeability (gj), indicating that the inside-outside potential of the junctional channel does not control gj. 4. Therefore, the steady-state junctional chord conductances were dependent only upon Vj. 5. The voltage dependence of the chord conductance was well fitted by a modified Boltzmann relation given by the equation (Formula: see text) with the constants: A = 0.15 +/- 0.03 mV-1 (n = 10) and V0 = 28 +/- 4 mV (n = 10); the latter two parameters were also found to be independent of both transmembrane potentials. 6. The junctional currents were already constant 1 ms after step changes in the junctional voltage; this was three orders of magnitude faster than the other known examples of voltage-controlled gap junctions between embryonic cells. 7. Our results may be interpreted by a highly voltage-dependent probability of opening of the junctional channels. They also suggest that the gap-junction channels forming the giant motor synapse respond very rapidly to potential and that the hemi-channels which constitute them may not be symmetric.

Action Potentials↗
PubMed1986

A calcium-activated sodium conductance contributes to the fertilization potential in the egg of the nemertean worm Cerebratulus lacteus.

The fertilization potential of the egg of the nemertean worm Cerebratulus lacteus consisted of a rapid shift from a resting potential of about -65 mV to a peak of about +44 mV; the peak was followed by a positive plateau at about +24 mV, lasting an average of 80 min. Reduction of extracellular calcium reduced the peak of the fertilization potential, indicating that the peak resulted from a calcium conductance, while reduction of extracellular sodium reduced the plateau potential, indicating that the plateau resulted from a sodium conductance. Microinjection of ethylene glycol bis(beta-aminoethyl ether)-N,N'-tetraacetic acid (EGTA) or 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA)/CaBAPTA buffers, having a free calcium concentration of less than or equal to about 0.1 microM lowered the fertilization potential plateau. Injection of a BAPTA/CaBAPTA mixture with a free calcium concentration of about 1 microM resulted in a prolonged positive potential at the level of the fertilization potential plateau. These observations indicated that the fertilization potential of the Cerebratulus egg depended on a calcium-activated sodium conductance. The plateau potential was reduced little, if any, when calcium-free seawater was perfused through the bath during the fertilization potential; nor was it reduced in seawater containing cadmium. These observations suggested the possibility that intracellular calcium stores could be important in producing the fertilization potential.

Animals↗
PubMed1986

A calcium-activated sodium conductance produces a long-duration action potential in the egg of a nemertean worm.

1. The egg of the nemertean worm Cerebratulus lacteus produced an action potential having a duration of about 9 min. We investigated the ionic conductances which accounted for this long-duration action potential. 2. The peak of the action potential was about +50 mV and depended on extracellular Ca2+, while the plateau potential was about +25 mV and depended on extracellular Na+. 3. Under voltage-clamp conditions, depolarization produced two temporally separate inward currents: a fast current which reached a peak at about 10 ms, and a slow current which took up to 1 min to reach its peak and lasted for several min. 4. The fast current was independent of extracellular Na+, but was blocked by removal of extracellular Ca2+. 5. The slow current was not seen when extracellular Na+ was replaced by choline+ or K+. 6. The slow current did not develop in Ca2+-free sea water, and was reduced to about half if Ca2+ was removed after the current had been initiated. 7. Microinjection of EGTA blocked the slow current, and reduced the action potential duration to about 1 min. 8. We concluded that a voltage-activated Ca2+ conductance produced the peak of the action potential, while a Ca2+-activated Na+ conductance produced its plateau.

Action Potentials↗
PubMed1985

Propagating potassium and chloride conductances during activation and fertilization of the egg of the frog, Rana pipiens.

Fertilization or artificial activation of the frog egg (Rana pipiens) elicits a positive-going shift in membrane potential which results from an opening of Cl- and K+ channels in the egg membrane. We examined the spatial localization of the currents produced by the opening of these channels, using large patch electrodes (tip diameters 3-10 microns). We also used small patch electrodes (tip diameters about 1 micron) to study the single K+ channel currents. After activation, with the patch electrode at any position on the egg surface, we observed a transient current, with a main peak lasting several seconds. This activation current occurred after a variable delay of 0-3 min following the rise of the activation potential. With 10% Ringer solution in the bath and pipette, the current was usually outward, although it sometimes had an inward component. With one patch electrode on the animal surface of the egg and another patch electrode on the vegetal surface, we observed that the activation current propagated over the egg surface. In experiments where the egg was activated by applying a hyperpolarizing pulse, the response in the animal half preceded that in the vegetal half by an average of about 1 min. The amplitude of the peak outward current was similar for animal and vegetal recordings (1-2 mA/cm2). Tetraethylammonium (11 mM) in the patch pipette blocked most of the outward component of the activation current and revealed an underlying inward component. The inward component of the activation current was carried by Cl-, since it could be reversed by raising the Cl- concentration in the pipette. The Cl- component of the activation current propagated over the egg surface, with timing similar to that of the total current. The average amplitude of the peak Cl- current was six or more times larger at the animal than the vegetal surface. Fertilization caused a current to propagate from the animal to the vegetal surface, like the current observed during activation. With a small patch electrode, single channel currents of the K+ component of the activation current could be seen. The probability that the channels were open increased at more positive potentials. The single channel conductance was estimated to be 25 pS, and the reversal potential to be -150 mV. Single Cl- channel currents have not yet been seen. Activation or fertilization of the frog egg resulted in a wave-like opening of Cl- and K+ channels, which spread from the animal to the vegetal half of the egg.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1984

Induction and disappearance of excitability in the oocyte of Xenopus laevis: a voltage-clamp study.

Electrically excitable, sodium-selective channels are induced in the membrane of the oocytes of Xenopus laevis when it is submitted to prolonged positive potentials (Kado, Marcher & Ozon, 1979; Baud, Kado & Marcher, 1982). Under a long positive voltage-clamp step, the membrane current, initially outward, becomes inward with a sigmoidal time course. The mean time to half-maximal inward current (t 1/2) is about 18 s at 16 degrees C when stepping the membrane potential to +55 mV. The rate of channel induction was very temperature dependent (Q10 about 5). In an Arrhenius plot, the t 1/2 for induction at temperatures between 5 and 22 degrees C showed a single slope. The rate of induction was dependent on the membrane potential, increasing exponentially with positive membrane potential (e-fold for a 20 mV change). When the membrane was maintained at resting potential after induction, the ability to produce inward currents with short depolarizing steps slowly disappeared with a t 1/2 of 4 min at 16 degrees C. The temperature dependence for disappearance was larger than that found for induction (Q10 about 7). The rate of disappearance was not dependent on holding the membrane potential in the range -30 to -100 mV. Induction proceeded in calcium-free medium. Cycloheximide, a potent protein synthesis inhibitor had no effect (100 micrograms/ml) on the induction rate. Isobutylmethylxanthine (IBMX) or theophyllin (phosphodiesterase inhibitors) applied externally (10(-4) M) did not affect the induction or disappearance rates. From the present results, mechanisms such as protein synthesis or a second messenger (such as calcium or cyclic AMP) do not appear to be involved. During the depolarization necessary to obtain induction, another conductance was also activated. It was more slowly established, appeared to be non-saturable and had a reversal potential between zero and -10 mV. It was found to be very much reduced at temperatures below about 16 degrees C.

Animals↗
PubMed1983

Application of antimony microelectrodes to intracellular pH monitoring.

Some novel studies of the properties of the antimony microelectrode used for intracellular pH measurements are described. First, it is shown that currents in the picoampere range, such as those encountered as leakage in some electrometers, induce important changes in pH sensitivity. The response time of the electrode has also been measured and indicates that the electrode exhibits a rapid time course which would be very useful for dynamic cytoplasmic pH investigations. An example of internal pH recording during cellular acidification in Xenopus laevis oocyte is also presented.

Animals↗
PubMed1982

Sodium channels induced by depolarization of the Xenopus laevis oocyte.

An electrically gated Na+ channel can be made to appear in the membrane of the Xenopus laevis oocyte by simple depolarization. This membrane normally responds passively to imposed transmembrane currents with resting potentials around -60 mV, but when it is held depolarized to more than about +30 mV it becomes possible to obtain long-lasting regenerative depolarizations up to +80 mV; these depolarizations can last as long as 20 min. This potential is due to an "induction" of a Na+-dependent channel that is electrically gated open and closed. Its threshold for opening is about -20 mV and it is selective for Na+ over Cs+ and choline+ but is blocked by relatively small quantities of Li+. When a long voltage clamp step to a positive potential under ENa (+70 to +90 mV) is applied, an inward current is observed for many minutes, implying that this channel does not have an inactivation mechanism. The inward Na+ current is blocked by 0.50 mM tetrodotoxin. When the membrane is held at or near resting potential, the excitability will disappear with time, but it can be made to reappear by again depolarizing the membrane.

Action Potentials↗
PubMed1981

The rise and fall of electrical excitability in the oocyte of Xenopus laevis.

1. An electrically excited (gated) sodium selective channel has been found in the Xenopus laevis oocyte, a cell membrane previously considered non-excitable. 2. The channel is produced by prolonged depolarization of the membrane and is removed by prolonged repolarization. Both processes are very dependent on temperature and potential. 3. Once produced, the channel can be opened and closed electrically, but does not show inactivation as is found in other sodium selective channels. 4. The sodium selectivity and the electrical gating properties of this channel make it a potentially useful candidate for the study of these general channel characteristics. The fact that this membrane can be made to show these properties reversibly offers the possibility of the studying the origins of this channels.

Animals↗
PubMed1979

Interaction between the horizontal vestibulo-ocular reflex and optokinetic response in rabbits.

Dynamic characteristics of the horizontal vestibulo-ocular reflex (HVOR), the optokinetic response (OKR), and their interactions were investigated in alert albino rabbits. For stimulation of the horizontal semicircular canals, the whole rabbit was rotated sinusoidally on a motor-driven turntable at peak-to-peak amplitudes of 5 degrees to 30 degrees over a frequency range of 1/30 to 1/2 Hz. Optokinetic stimulation was provided by a narrow vertical slit light source presented in front of the eye to be tested. The evoked horizontal eye movements were observed and measured by means of a closed circuit television system adapted to provide an analog signal proportional to the eye movement. The net HVOR was obtained by rotation of the turntable in darkness and the net OKR by rotation of the light source. Combining rotation of the turntable with a stationary light source immediately increased the gain and reduced the phase shift of the HVOR. The light source moving in phase with the turntable, but at twice the angular amplitude, reduced the gain and advanced the phase of the HVOR. Eye movement curves of the HVOR modified by a fixed or moving slit light could be reconstructed approximately by a linear combination of the net HVOR and OKR.

Animals↗
PubMed1979

On the fibers of the III, IV and VI cranial nerves of the cat.

The fiber content and diameter spectra of the cranial nerves III, IV and VI were analysed in cat. A semi-automatic technique of measuring fiber diameters is presented and compared to the manual method. The number of fibres was counted in the proximal part of the three main nerves and in each of their distal branches before they enter the EOM. Compared to the muscle weight, the branch to the RB had fewer fibers than all the other muscle branches. The diameter spectra of the proximal part of the three main nerves were compared with the diameter spectra of each of their distal branches. Minor differences were found among them. Only the RB had a striking difference in the spectrum which was skewed toward the large diameters.

Abducens Nerve↗
PubMed1977

Permeability, phase-boundary potential and conductance in a cholinergic channel without constant field.

A potassium-selective, chemically excitable channel, whose characteristics cannot be accurately described by constant-field theory, is studied by a new approach based on diffusion theory but with no need for the classical assumptions of constant field, homogeneous membrane, and equal phase-boundary potentials at both interfaces. Permeability is defined, free of these constraints, and the Goldman coefficient is demonstrated to be a special case useful only when the constraints apply. Permeability can be evaluated directly from current-voltage data, and it is found not to be a parameter in this channel, but rather a function of both the voltage and the concentration of the permeant ion. However, it becomes concentration-independent when the membrane voltage is equal to the sum of the phase-boundary potentials. That sum can therefore be determined from these data, and it is -65 mV in this channel. The permeability at that potential is a channel parameter, and equal to 8.66 X 10(-6) cm/s for this channel. A constant field is shown not to exist in this channel and the Goldman coefficient not to be a parameter but a function of potential and concentration. Although errors introduced into this coefficient by nonconstant field and unequal surface potentials partially cancel each other, the coefficient is nevertheless not a correct measure of permeability.

Animals↗
PubMed1977

Permeability and phase-boundary potentials determined from conductance in a transmitter-activated potassium channel in Aplysia californica in the absence of a constant field.

A potassium-selective, chemically excitable channel, whose characteristics cannot be accurately described by "constant field" theory, is studied using a new approach based on diffusion theory but having no need for the classical assumptions of constant field, homogeneous membrane, and equal phase-boundary potentials at both interfaces. Permeability is defined, free of these constraints, and the Goldman coefficient is demonstrated to be a special case useful only when the constraints apply. Permeability can be evaluated directly from chord conductance, and it is found not to be a parameter in this channel, but rather a function of both the voltage and the concentration of the permeant ion. However, it becomes concentration-independent when the membrane voltage is equal to the sum of the phase-boundary potentials. That sum can therefore be determined from these data, and it is -65 mV in this channel. The permeability at that potential is a channel parameter, and equal to 8.77 (10)-6 cm/sec for this channel. A constant field is shown not to exist in this channel, and the Goldman coefficient not to be a parameter but a function of potential and concentration. Although errors introduced into this coefficient by nonconstant field and unequal surface potentials partially cancel each other, the coefficient is nevertheless not a correct measure of permeability.

Animals↗
PubMed1975

Voltage-current relationship of a carbachol-induced potassium-ion pathway in Aplysia neurones.

1. The electrical characteristics of a potassium ion selective pathway produced by the action of carbachol on Aplysia neurones (Kehoe, 1972b) has been studied. 2. The relationship between current and voltage has been found to be non-linear, the conductance increasing with depolarization and decreasing with hyperpolarization. The degree of rectification was reduced when the external potassium was raised to 50 mM from its normal value of 10 mM. 3. The direction of the rectification and the effect of increased potassium are as predicted by the 'constant field' theory, but the degree of rectification is somewhat larger.

Animals↗
PubMed1973

Aplysia giant cell: soma-axon voltage clamp current differences.

Under voltage clamp, local membrane currents have been measured in several regions of the soma. The early inward current appears to pass largely through the membrane of the axon and of the soma near the axon in normal media. After 10(-5) molar tetrodotoxin (TTX) is added to the bathing medium the larger inward current is found in the somatic membrane away from the axon. The late currents are larger at the soma in both normal and TTX media.

Animals↗