Potassium currents in frog ventricular muscle: evidence from voltage clamp currents and extracellular K accumulation

The Journal of Physiology
L Cleemann, M Morad


1. The single sucrose voltage clamp technique was used to control the membrane potential of strips of frog ventricular muscle and to measure the membrane current. The extracellular K accumulation was estimated from the after-potential observed after the release of the voltage clamp. 2. Comparing the time course of the membrane current to the time course of the development of the after-potential at different membrane potentials, it was found that all slow current changes are related to changes in the K current across the membrane. 3. Based on measurements of membrane current and the after-potential, the total membrane current was separated into two fractions: (a) the K current which gives rise to K accumulation and (b) the residual membrane current which is unrelated to K accumulation. The current-voltage relation for the residual membrane current is linear or slightly inwardly-rectifying. Residual current is zero at the resting potential and increases to about 1 microamperemeter/cm2 at -20 mV. 4. The measured membrane currents and after-potentials indicate qualitative differences between the K currents which dominate below and above -20 mV. More negative to -20 mV the after-potential develops rapidly while at potentials positiv...Continue Reading


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