Biomaterial Database

The effect of heart rate on the arrhythmogenic transient inward current in isolated sheep cardiac Purkinje fibres. 1990

B Henning, and M R Boyett

Department of Cardiology, University of Freiburg, FRG.

1. The effect of heart rate on the arrhythmogenic transient inward current (ITI) has been studied in sheep cardiac Purkinje fibres. 2. Transient inward current and force (active force, tonic force and the after-contraction) have been measured in voltage-clamped preparations. Intracellular Na+ activity (aiNa) was measured simultaneously using Na(+)-sensitive microelectrodes. The effects of changes in voltage-clamp pulse frequency on the ITI amplitude, active force, tonic force, the after-contraction and aiNa have been investigated in different bathing solutions. 3. After a stepwise increase in pulse rate there was a biphasic response of ITI amplitude: a short-lasting (50 s) phase during which ITI amplitude increased followed by a decline in ITI amplitude. The second phase could be fitted by an exponential with a time constant between 102 and 184 s. The after-contraction changed in a similar biphasic manner whereas force and aiNa declined monophasically; active force first declined, increased and then declined again. These changes were greater at faster rates of pulsing. 4. Linear relationships between ITI amplitude, after-contraction amplitude and tonic force were observed in all experiments. 5. In K(+)-free solution the response of the ITI was markedly changed. After an increase in pulse rate the initial increase in ITI was enhanced, whereas the subsequent decline was strongly reduced or even abolished. Potassium-free solution blocks the Na+ pump, and activation of the Na+ pump by addition of Cs+ or K+ restored the phase of decay of ITI amplitude during rapid stimulation. 6. A reduction of external Na+ to about 50% or elevation of external Ca2+ increased ITI but had little effect on the rate-dependent changes in the current. 7. When stimulation was resumed at the basic pulse rate after a period of rapid pulsing the ITI amplitude initially continued to decline: this was followed by a slow recovery (over 10-15 min) of ITI amplitude back to its steady-state value prior to fast pulsing. 8. These results are consistent with the hypothesis that changes of ITI are the result of rate-dependent changes in intracellular Ca2+, which in turn are in part dependent on changes of intracellular Na+.

UI	MeSH Term	Description	Entries
D008954	Models, Biological	Theoretical representations that simulate the behavior or activity of biological processes or diseases. For disease models in living animals, DISEASE MODELS, ANIMAL is available. Biological models include the use of mathematical equations, computers, and other electronic equipment.	Biological Model,Biological Models,Model, Biological,Models, Biologic,Biologic Model,Biologic Models,Model, Biologic
D009200	Myocardial Contraction	Contractile activity of the MYOCARDIUM.	Heart Contractility,Inotropism, Cardiac,Cardiac Inotropism,Cardiac Inotropisms,Contractilities, Heart,Contractility, Heart,Contraction, Myocardial,Contractions, Myocardial,Heart Contractilities,Inotropisms, Cardiac,Myocardial Contractions
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
D002118	Calcium	A basic element found in nearly all tissues. It is a member of the alkaline earth family of metals with the atomic symbol Ca, atomic number 20, and atomic weight 40. Calcium is the most abundant mineral in the body and combines with phosphorus to form calcium phosphate in the bones and teeth. It is essential for the normal functioning of nerves and muscles and plays a role in blood coagulation (as factor IV) and in many enzymatic processes.	Coagulation Factor IV,Factor IV,Blood Coagulation Factor IV,Calcium-40,Calcium 40,Factor IV, Coagulation
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
D006329	Heart Conduction System	An impulse-conducting system composed of modified cardiac muscle, having the power of spontaneous rhythmicity and conduction more highly developed than the rest of the heart.	Conduction System, Heart,Conduction Systems, Heart,Heart Conduction Systems,System, Heart Conduction,Systems, Heart Conduction
D006339	Heart Rate	The number of times the HEART VENTRICLES contract per unit of time, usually per minute.	Cardiac Rate,Chronotropism, Cardiac,Heart Rate Control,Heartbeat,Pulse Rate,Cardiac Chronotropy,Cardiac Chronotropism,Cardiac Rates,Chronotropy, Cardiac,Control, Heart Rate,Heart Rates,Heartbeats,Pulse Rates,Rate Control, Heart,Rate, Cardiac,Rate, Heart,Rate, Pulse
D000200	Action Potentials	Abrupt changes in the membrane potential that sweep along the CELL MEMBRANE of excitable cells in response to excitation stimuli.	Spike Potentials,Nerve Impulses,Action Potential,Impulse, Nerve,Impulses, Nerve,Nerve Impulse,Potential, Action,Potential, Spike,Potentials, Action,Potentials, Spike,Spike Potential
D000254	Sodium-Potassium-Exchanging ATPase	An enzyme that catalyzes the active transport system of sodium and potassium ions across the cell wall. Sodium and potassium ions are closely coupled with membrane ATPase which undergoes phosphorylation and dephosphorylation, thereby providing energy for transport of these ions against concentration gradients.	ATPase, Sodium, Potassium,Adenosinetriphosphatase, Sodium, Potassium,Na(+)-K(+)-Exchanging ATPase,Na(+)-K(+)-Transporting ATPase,Potassium Pump,Sodium Pump,Sodium, Potassium ATPase,Sodium, Potassium Adenosinetriphosphatase,Sodium-Potassium Pump,Adenosine Triphosphatase, Sodium, Potassium,Na(+) K(+)-Transporting ATPase,Sodium, Potassium Adenosine Triphosphatase,ATPase Sodium, Potassium,ATPase, Sodium-Potassium-Exchanging,Adenosinetriphosphatase Sodium, Potassium,Pump, Potassium,Pump, Sodium,Pump, Sodium-Potassium,Sodium Potassium Exchanging ATPase,Sodium Potassium Pump