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PubMed1978

Cole-Moore effect in the frog node.

Potassium currents were recorded from the voltage-clamped frog node (Rana esculenta) during various test pulses that followed hyperpolarizing prepulses of different amplitudes and durations. Both the delay in potassium current onset and the shape of the current trace as a function of time were found to be a function of prepulse parameters. This finding is different from the current trace superposition described by Cole and Moore for a specific test pulse, sodium equilibrium potential in the squid giant axon. The Cole-Moore effect, which was found here only under a specific set of conditions, thus may be a special case rather than the general property of the membrane. The implication of these findings to the various excitable membrane potassium channel models, which are based on the Cole-Moore effect, is discussed.

Animals↗

PubMed1976

Effect of conditioning potential on potassium current kinetics in the frog node.

The kinetics of potassium conductance changes were determined in the voltage clamped frog node (Rana esculenta), as a function of conditioning prepotential. The conditioning potential duration varied from 1 to 50 ms and the amplitude between -60 and +130 mV (relative to rest). The conductance kinetics were determined at a single test potential of +20 mV (depolarization) by means of the slope of log [ninfinity - nt] vs. time relationship which defines the time constant of the process (tau). The values of tau, after conditioning hyperpolarizations, were around 5 ms, up to 10 times greater than values obtained following a strong depolarization. The tau vs. pre-potential curve was sigmoid in shape. These differences were only slightly dependent on [K+]0 or conditioning pulse duration. The steady-state current values were also found to be a function of conditioning potential. After conditioning hyperpolarizations, the log [ninfinity - nt] vs. time curve could not be fitted by a single exponent regardless of the power of n chosen. The prepotential dependency of potassium current kinetics is inconsistent with the Hodgkin-Huxley axon model where the conductance parameters are assumed to be in either one of two possible states, and where the rate of transfer from one state to the other follows first order kinetics. In contrast the described kinetics may be consistent with complex multistate potassium "channel" models or membranes consisting of a number of types of channels.

Animals↗