Physiological implications of K accumulation in heart muscle.
K+-selective microelectrodes in conjugation with the voltage clamp technique were used to examine the voltage and time dependence of K+ efflux and accumulation in cardiac muscle. K+ efflux per action potential is about 10 to 30 pmoles/cm2 per sec. Accumulation of K+ in the paracellular space plays an important role in regulation of action potential duration, so that the [K+]o prior to generation of an action potential determines the duration of following action potential. This regulation is brought about by the shift of inward rectifying K+ current along the voltage axis, so at higher [K+]o there is more outward current at plateau potentials. Monitoring [K+]o after a period of rapid beating provides quantitative data regarding Na-pump activity. The data suggest the Na-pump is electrogenic, making it difficult to assess the extent of K+ accumulation from the measurements of resting potential alone. These studies indicate that changes in [K+]o not only reflect outward membrane currents and Na-pump activity, but also play an important physiological regulatory role in determining the duration of the action potential.
D000200:Action Potentials; D000818:Animals; D001001:Anura; D001693:Biological Transport, Active; D005110:Extracellular Space / Q000378:metabolism; D006321:Heart / Q000502:physiology*; D006352:Heart Ventricles / Q000378:metabolism; D066298:In Vitro Techniques; D008564:Membrane Potentials; D009200:Myocardial Contraction; D009206:Myocardium / Q000378:metabolism*; D011188:Potassium / Q000502:physiology*; D011817:Rabbits; D012849:Sinoatrial Node / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism
D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium