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Biomedical subjects

H Irisawa

Publications and source records attributed to H Irisawa.

At least 73 records · Page 4Linked to original sources
PubMed1976

Membrane currents in the rabbit sinoatrial node cell as studied by the double microelectrode method.

When a strand of the rabbit sinoatrial node tissue was shortened by ligation, the spatial decay of electrotonic potential decreased and the input impedance increased. In a piece of the tissue 0.2-0.3 mm in diameter apparently uniform current spread was obtained. Action potentials recorded from three different sites in this small piece occurred simultaneously and were superimposable. In voltage clamp experiments using the double microelectrode method, the membrane potential was usually held at -30 to -40 mV, where no net current flowed. When membrane potential was suddenly changed from the holding potential, the sign and the time course of the ionic current varied with membrane potential. Hyperpolarization gave an inward current which increased with time. Depolarization gave a transient inward current followed by sustained outward current, and repolarization gave an outward current tail which exponentially subsided with a time constant of 0.37 s. The membrane time constant was 12.0 ms. When the specific membrane capacitance was assumed to be 1 muF/cm2, the specific membrane resistance at the resting potential was 12 Komega cm2. The peak of the transient inward current on depolarization was 1.3 X 10(-5) A/cm2.

Action Potentials↗
PubMed1976

Contracture and hyperpolarization of the rabbit sinoatrial node cells in Na-depleted solution.

A study was made on both hyperpolarization and contracture which developed in the rabbit sinoatrial node cell during perfusion with Na-depleted solution. The membrane was hyperpolarized in 19 out of 27 specimens (-69.5 +/- 6.0 mV), while in the remaining 8 specimens the value of the membrane potential remained low (-39.4 +/- 2.7 mV). Slope conductance increased as the membrane was hyperpolarized in Na-depleted solution, but not when the value of the membrane potential remained at low. The amplitude of hyperpolarization increased with decrease in Na concentration, increase in Ca concentration and increase in perfusate temperature. A marked increase in diastolic tension was observed in 23 out of 29 specimens but in the 6 remaining specimens the increase in tension was small. Tension increased with decrease in Na concentration, increase in Ca concentration, and increase in perfusate temperature. Pretreatment with ouabain caused a consistent increase in contracture tension, while its effect on the membrane hyperpolarization was variable among different specimens. These results may be explained by assuming that intracellular Ca concentration increased with Na-Ca exchange in Na-depleted solution. In addition to contracture, increase in intracellular Ca concentration might have caused an increase of membrane K conductance and produced marked hyperpolarization.

Animals↗
PubMed1976

Effects of calcium ion on the rising phase of the action potential in rabbit sinoatrial node cells.

To clarify the role of Ca ion in the rising phase of the sinoatrial (S-A) node action potential, the sigmoidal relationship between the maximum rate of rise of the action potential and the maximum diastolic potential was examined at various concentrations of Ca. The membrane potential was changed by applying a current across a single sucrose gap. The sigmoidal curve shifted toward the positive potential without a change in maximum value when the Ca concentration was increased from nominal "zero" to 10 mM. Therefore, it is concluded that Ca ion modifies the inactivation process of Na current which is responsible for the rapid rising phase of the S-A node action potential. The duration of the action potential and the maximum diastolic potential were decreased with an increase in Ca concentration. The observation that the overshoot of the action potential increased by 12 mV for a tenfold increase in concentration of Ca (within the range of 0.1-5.0 mM) suggests that the inward current of Ca ion may be responsible for the overshoot of the S-A node action potential.

Action Potentials↗
PubMed1975

Contribution of an electrogenic sodium pump to the membrane potential in rabbit sinoatrial node cells.

A study has been made of the transient hyperpolarization (K+-induced hyperpolarization) which developed following readmission of potassium after having pre-treated the rabbit sinoatrial node tissue with K+-depleted Tyrode solution for 4--5 min at 35 degrees C. Evidence is presented indicating that the K+-induced hyperpolarization results from the activity of an electrogenic sodium pump: The K+-induced hyperpolarization was inhibited by substituting Li+ for Na+ and by cooling the tissue. The amplitude of the K+-induced hyperpolarization was increased either by increasing K+ concentration in the recovery solution or by decreasing K+ concentration in the pre-treatment K+-depleted solution. By removing Cl- from the perfusates, the amplitude of the K+-induced hyperpolarization increased. In a Cl--depleted solution, the sinoatrial node cell membrane hyperpolarized by approximately 15 mV without a transient depolarization.

Animals↗
PubMed1975

Effects of Na+ and K+ on the resting membrane potential of the rabbit sinoatrial node cell.

To estimate the "resting potential" of the sinoatrial node cell, membrane potentials in quiescent states under various conditions were compared with the holding potential at which no net membrane current flowed during the voltage clamp. The membrane potential of the rabbit sinoatrial node cell was recorded using a conventional microelectrode method. The single sucrose gap method and the double microelectrode method were employed for the voltage clamp. The membrane potential immediately before the resumption of the spontaneous activity in normal Tyrode solution after a quiescence in high K+ concentration, in low Na+ concentration or in low temperature was approximately - 37 m V and was similar to that of the temporarily quiescent sinoatrial node cells after dissection. The holding potential at which no net membrane current flowed was - 38.4 m V, which coincided with the membrane potential during quiescence. The resting potential in quiescence increased by approximately 17 m V for a tenfold decrease in the extracellular Na+ concentration, and 22 m V for a tenfold increase in the K+ concentration. The relative membrane conductance decreased transiently on removing Na+ from the bathing medium. These findings suggest that a potential equivalent to the resting potential existss in the S-A node cell approximately 20 m V positive to the maximum diastolic potential, and this low value might be due to the high Na+ conductance of the cell membrane.

Animals↗
PubMed1974

The effect of polarization on the action potentials of the rabbit AV nodal cells.

The resting potential of various parts of the AV nodal regions of an excised rabbit heart was changed by applying constant electrical current with a suction electrode. The membrane potential was recorded with an intracellular microelectrode and the maximum rate of rise of depolarization was computed. The action potential recorded from the AV nodal cell responded to constant current in a manner qualitatively similar to other myocardiums. The relationship between resting potential and amplitude of action potential was expressed by a straight line, while a sigmoidal relationship was observed between the resting potential and the maximum rate of rise of depolarization. Most of the initial current system in alpha region was inactivated at the control membrane potential. The maximum value of the maximum rate of rise of depolarization of alpha region was 30 V/sec which was lower than that of other parts of the nodal region.

Action Potentials↗
PubMed1974

The effect of sodium ion on the initial phase of the sinoatrial pacemaker action potentials in rabbits.

The maximum rate of rise of depolarization of the isolated rabbit S-A node cells was studied with an intracellular microelectrode. Both the amplitude and the maximum rate of rise of depolarization reduced in proportion to the extracellular sodium concentration, but the reduction in the maximum rate of rise of depolarization was greater than that in the amplitude of action potentials. The frequency of spontaneous activities and the duration of action potentials were increased during application of depolarizing current, while they were both reduced during application of hyperpolarizing current. Both the amplitude of the action potential and the maximum rate of rise of depolarization showed voltage dependent characteristics. The maximum value of the maximum rate of rise of depolarization in pacemaking cells ranged from 2 to 11 V/sec and was quantitatively lower than other myocardial fibers. The maximum value of the maximum rate of rise of depolarization in 50% Na+ solution was reduced to approximately 1/2 of the control in normal Na+ solution. A signoidal relationship was observed between the membrane potential and the maximum rate of rise of depolarization. When the temperature of the perfusate was lowered, the signoidal curve shifted toward the negative direction. It is concluded that sodium ion is responsible for the generation of the initial phase of the S-A node action potentials, as in other myocardial cells. However, the amount of ionic current required for spike generation is quantitatively smaller than other myocardial cells.

Action Potentials↗