Biomaterial Database

Pacemaker current, membrane resistance, and K+ in sheep cardiac Purkinje fibres. 1992

M Vassalle, and H Kotake, and C I Lin

Department of Physiology, State University of New York, Brooklyn 11203.

OBJECTIVE The pacemaker current in cardiac Purkinje fibres has been attributed to either a decrease in potassium conductance or an increase in a non-specific (Na-K) conductance. The former mechanism would be associated with an increase in membrane resistance (Rm) and the latter with a decrease in Rm. The aim of this study was to obtain evidence in support of one or other mechanism by measuring Rm during the pacemaker current (Idd) under conditions where there is a small or no extracellular potassium depletion. METHODS Hearts were obtained from anaesthetised sheep and thin strands of ventricular Purkinje fibres were shortened to less than or equal to 1.6 mm. Purkinje fibres were voltage clamped to potentials positive and negative to the potassium equilibrium potential (EK) using a two microelectrode technique. Small current pulses were superimposed on Idd to measure Rm changes. Procedures were used that decrease either the background potassium current IKl or Idd in order to dissect changes in Rm due to K depletion from those due to Idd. RESULTS Rm increased during Idd, whether the pacemaker current increased or decreased as a function of time. Increasing [K]o from 2.7 to 5.4 mmol.litre-1 decreased Rm and during hyperpolarising steps increased the instantaneous current but did not change Idd amplitude. In 2.7 mmol.litre-1 K, caesium (Cs, 2 mmol.litre-1) increased the holding current (Ih), had little effect on the instantaneous current, and eliminated Idd and associated Rm changes. In 5.4 and 10.8 mmol.litre-1 K, Cs increased Ih and decreased Idd amplitude and in 10.8 mmol.litre-1 K Cs decreased the instantaneous current on hyperpolarisation. If the current was reversed, Cs decreased but did not abolish it. In normal [K]o, barium (Ba, 0.05-0.5 mmol.litre-1) increased Ih and Rm, reduced the instantaneous current but did not increase Idd amplitude. In high [K]o, Ba instead increased the amplitude and rate of development of Idd. When Cs was applied in the presence of Ba, Idd was reduced or eliminated depending on [K]o. CONCLUSIONS The changes in membrane resistance during the pacemaker current cannot be accounted for by K depletion and suggest that in the range of diastolic depolarisation the pacemaker current results predominantly from a time dependent decrease in K conductance.

UI	MeSH Term	Description	Entries
D008297	Male		Males
D008564	Membrane Potentials	The voltage differences across a membrane. For cellular membranes they are computed by subtracting the voltage measured outside the membrane from the voltage measured inside the membrane. They result from differences of inside versus outside concentration of potassium, sodium, chloride, and other ions across cells' or ORGANELLES membranes. For excitable cells, the resting membrane potentials range between -30 and -100 millivolts. Physical, chemical, or electrical stimuli can make a membrane potential more negative (hyperpolarization), or less negative (depolarization).	Resting Potentials,Transmembrane Potentials,Delta Psi,Resting Membrane Potential,Transmembrane Electrical Potential Difference,Transmembrane Potential Difference,Difference, Transmembrane Potential,Differences, Transmembrane Potential,Membrane Potential,Membrane Potential, Resting,Membrane Potentials, Resting,Potential Difference, Transmembrane,Potential Differences, Transmembrane,Potential, Membrane,Potential, Resting,Potential, Transmembrane,Potentials, Membrane,Potentials, Resting,Potentials, Transmembrane,Resting Membrane Potentials,Resting Potential,Transmembrane Potential,Transmembrane Potential Differences
D011188	Potassium	An element in the alkali group of metals with an atomic symbol K, atomic number 19, and atomic weight 39.10. It is the chief cation in the intracellular fluid of muscle and other cells. Potassium ion is a strong electrolyte that plays a significant role in the regulation of fluid volume and maintenance of the WATER-ELECTROLYTE BALANCE.
D011690	Purkinje Fibers	Modified cardiac muscle fibers composing the terminal portion of the heart conduction system.	Purkinje Fiber,Fiber, Purkinje,Fibers, Purkinje
D002586	Cesium	A member of the alkali metals. It has an atomic symbol Cs, atomic number 55, and atomic weight 132.91. Cesium has many industrial applications, including the construction of atomic clocks based on its atomic vibrational frequency.	Caesium,Caesium-133,Cesium-133,Caesium 133,Cesium 133
D003971	Diastole	Post-systolic relaxation of the HEART, especially the HEART VENTRICLES.	Diastoles
D004594	Electrophysiology	The study of the generation and behavior of electrical charges in living organisms particularly the nervous system and the effects of electricity on living organisms.
D005260	Female		Females
D000818	Animals	Unicellular or multicellular, heterotrophic organisms, that have sensation and the power of voluntary movement. Under the older five kingdom paradigm, Animalia was one of the kingdoms. Under the modern three domain model, Animalia represents one of the many groups in the domain EUKARYOTA.	Animal,Metazoa,Animalia
D001464	Barium	An element of the alkaline earth group of metals. It has an atomic symbol Ba, atomic number 56, and atomic weight 138. All of its acid-soluble salts are poisonous.