Biomaterial Database

Rate-limiting mechanisms of exchange reactions in the cardiac sarcolemma Na(+)-Ca2+ exchanger. 1995

D Khananshvili, and G Shaulov, and E Weil-Maslansky

Department of Physiology and Pharmacology, Sackler School of Medicine, Tel-Aviv University, Ramat-Aviv, Israel.

The effects of temperature, pH, voltage and K+ were tested on Na(+)-Ca2+ and Ca(2+)-Ca2+ exchanges with a goal to elucidate the rate-limiting mechanisms. The initial rates (t = 1 s) of Nai- and Cai-dependent 45Ca uptakes were measured in the sarcolemma vesicles. At pH 7.4 the Ca(2+)-Ca2+ exchange shows a bell-shaped temperature curve with a maximum at 27-29 degrees C. This effect is not caused by irreversible inactivation of the exchanger. The increase of pH from pH 6.0 to 7.4 in the K(+)-free medium decelerates the Ca(2+)-Ca2+ exchange 1.5-2.0-fold, while the addition of K+ accelerates the Ca(2+)-Ca2+ exchange 2.0-3.0-fold. Therefore, the accelerating effect of K+ opposes the decelerating effect of deprotonation. Temperatures increase (6-45 degrees C) in the K(+)-free medium (pH 7.4) elevates the Na(+)-Ca2+/Ca(2+)-Ca2+ exchange ratio from 0.8 to 5.0. With varying temperatures (6-37 degrees C) and pH 5.0-9.7, K+ has no considerable effect on Na(+)-Ca2+ exchange but accelerates the Ca(2+)-Ca2+ exchange 2-3-fold. At 6-45 degrees C and fixed pH 7.4, the inside-positive potential (delta psi > or = +200 mV) accelerates the Na(+)-Ca2+ exchange 1.7-2.0-fold, suggesting that the same rate-limiting reaction controls the Na(+)-Ca2+ exchange at various temperatures. It is concluded that (a) At pH > 6.5 (6-45 degrees C and 0-100 mM K+) the voltage-sensitive Na+ efflux limits the Na(+)-Ca2+ exchange, while the Ca2+ efflux limits the Ca(2+)-Ca2+ exchange.(ABSTRACT TRUNCATED AT 250 WORDS)

UI	MeSH Term	Description	Entries
D007700	Kinetics	The rate dynamics in chemical or physical systems.
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
D009206	Myocardium	The muscle tissue of the HEART. It is composed of striated, involuntary muscle cells (MYOCYTES, CARDIAC) connected to form the contractile pump to generate blood flow.	Muscle, Cardiac,Muscle, Heart,Cardiac Muscle,Myocardia,Cardiac Muscles,Heart Muscle,Heart Muscles,Muscles, Cardiac,Muscles, Heart
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.
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
D002352	Carrier Proteins	Proteins that bind or transport specific substances in the blood, within the cell, or across cell membranes.	Binding Proteins,Carrier Protein,Transport Protein,Transport Proteins,Binding Protein,Protein, Carrier,Proteins, Carrier
D002417	Cattle	Domesticated bovine animals of the genus Bos, usually kept on a farm or ranch and used for the production of meat or dairy products or for heavy labor.	Beef Cow,Bos grunniens,Bos indicus,Bos indicus Cattle,Bos taurus,Cow,Cow, Domestic,Dairy Cow,Holstein Cow,Indicine Cattle,Taurine Cattle,Taurus Cattle,Yak,Zebu,Beef Cows,Bos indicus Cattles,Cattle, Bos indicus,Cattle, Indicine,Cattle, Taurine,Cattle, Taurus,Cattles, Bos indicus,Cattles, Indicine,Cattles, Taurine,Cattles, Taurus,Cow, Beef,Cow, Dairy,Cow, Holstein,Cows,Dairy Cows,Domestic Cow,Domestic Cows,Indicine Cattles,Taurine Cattles,Taurus Cattles,Yaks,Zebus
D006863	Hydrogen-Ion Concentration	The normality of a solution with respect to HYDROGEN ions; H+. It is related to acidity measurements in most cases by pH	pH,Concentration, Hydrogen-Ion,Concentrations, Hydrogen-Ion,Hydrogen Ion Concentration,Hydrogen-Ion Concentrations
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
D012964	Sodium	A member of the alkali group of metals. It has the atomic symbol Na, atomic number 11, and atomic weight 23.	Sodium Ion Level,Sodium-23,Ion Level, Sodium,Level, Sodium Ion,Sodium 23