A New Interpretation of the Dynamic Changes of the Potassium Conductance in the Squid Giant Axon

Tille, J.

doi:10.1016/s0006-3495(65)86708-x

Cited by 26 publications

(11 citation statements)

References 2 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Various authors have proposed theories of channel gating that postulate interactions among channels. The theories of Tille (1965); Adam (1960) and Hill & Chen (1971) assume cooperative interactions among channels that form a regular array in the membrane, and Tille has shown that the high order kinetics of the Cole & Moore (1960) hyperpolarization delay could be explained by such a theory. Changeux, Thiery, Tung & Kittel (1967) have presented a theory of cooperativity among membrane-bound enzymes which, if applied to ionic channels, would explain the steep voltage-dependence of activation without requiring a large dipole moment in each channel macromolecule.…”

Section: Discussionmentioning

confidence: 99%

The conductance of sodium channels under conditions of reduced current at the node of Ranvier.

Sigworth¹

1980

The Journal of Physiology

View full text Add to dashboard Cite

2. Reduction of the sodium current by depolarizing prepulses had no effect on y, and, in cases where it could be determined, had no significant effect on N. Partial block of the sodium conductance with tetrodotoxin and saxitoxin also did not affect y significantly, but reduced N.3. y was reduced to about 40 % of the control value at -5 mV when the pH of the external solution was reduced to 5 0. The pH dependence of y is consistent with the theories of Woodhull and of Drouin & Neumcke.4. The differing effects of prepulses, toxins and pH are interpreted in view of the different time scales of channel inactivation or block under these conditions. 5. The nearly unchanged y with prepulses and partial toxin block provides further evidence for the absence of interactions among sodium channels.

show abstract

Section: Discussionmentioning

confidence: 99%

The conductance of sodium channels under conditions of reduced current at the node of Ranvier.

Sigworth¹

1980

The Journal of Physiology

View full text Add to dashboard Cite

show abstract

“…However, n~ is not at all well described in this way, since it continues to increase slowly over tens of millivolts beyond the range of potentials at which it is steeply dependent on E,~. Perhaps this is another reason for suspecting that there might be a better formulation for those currents with a sigmoid time course of activation; we have not pursued this question, although Tille (1965) has presented an alternative approach which does not use power functions.…”

Section: Voltage Dependence Of Equilibrium Constantmentioning

confidence: 99%

A transition state theory approach to the kinetics of conductance changes in excitable membranes

Tsien¹,

Noble²

1969

J. Membrain Biol.

View full text Add to dashboard Cite

The kinetics of ionic current mechanisms in excitable membranes are analyzed. It is assumed that there are voltage-dependent reactions occurring in the membrane which are independent of the flow of ionic current. The experimental evidence for this assumption is reviewed in the light of more recent results on the kinetics of conductance changes in cardiac membranes. Rate equations are then obtained using transition state theory and assuming that each reaction is rate limited by only one energy barrier. These equations give simple exponential functions for the voltage dependence of the rates. More complex functions may be obtained by assuming that more than one energy barrier is rate limiting. The single-barrier equations are used to estimate the energies of formation of the transition state. In most cases, the entropy of formation is positive but there is no systematic order in the estimated enthalpies. These results are contrasted with those for the ion permeation process itself which normally has a negative entropy of activation. This contrast reinforces the assumption that the reactions controlling membrane permeability are distinct from the ion permeation process itself. The significance of the positive entropy of formation of the transition state in the permeability reactions is discussed, and it is suggested that the membrane structures underlying these reactions may change their degree of hydration during the formation of the transition state.

show abstract

“…Nonlinear differential equations describe the potassium conductance. An example of such a description is given by Tille (1965).…”

mentioning

confidence: 99%

Conditioning prepulses and kinetics of potassium conductance in the frog node

Bruin

1982

J. Membrain Biol.

View full text Add to dashboard Cite

The kinetics of potassium conductance were analyzed in response to voltage-clamp steps with holding potential (-75 mV) as initial condition and after a positive prepulse towards +45 mV of 10-msec duration. As the potassium reversal potential EK altered during potassium current flow, a method to obtain the conductance independent of EK was used. Conductance kinetics at 15 degrees C were analyzed according to the Hodgkin-Huxley (HH) model. The time constant of potassium activation, with holding potential as initial condition, is a monotonous decreasing function of membrane potential. Its value of ca. 9 msec at -50 mV decreases to 1 msec at +30 mV. Changes in EK did not affect the voltage dependency of this time constant. The time constant of potassium deactivation, i.e. the off-response following a 10-msec prepulse towards +45 mV, shows a completely different voltage dependency. At a membrane potential of -90 mV it is approximately 2 msec and gradually increases for more positive voltages towards a maximum value of about 6 msec, that is reached between -5 and 0 mV. At still larger values of membrane voltage this time constant starts to fall again. It is concluded that a HH-model, as applied for a single population of potassium channels, has to be rejected. Computer simulations indicate that an extension to two populations of independent potassium channels, each with HH-kinetics, is also inconsistent with the observed results.

show abstract

A New Interpretation of the Dynamic Changes of the Potassium Conductance in the Squid Giant Axon

Cited by 26 publications

References 2 publications

The conductance of sodium channels under conditions of reduced current at the node of Ranvier.

The conductance of sodium channels under conditions of reduced current at the node of Ranvier.

A transition state theory approach to the kinetics of conductance changes in excitable membranes

Conditioning prepulses and kinetics of potassium conductance in the frog node

Contact Info

Product

Resources

About