Biomaterial Database

Calcium-induced release of strontium ions from the sarcoplasmic reticulum of rat cardiac ventricular myocytes. 1997

C I Spencer, and J R Berlin

Bockus Research Institute, Graduate Hospital, Philadelphia, PA 19146, USA. crspence@mail.med.upenn.edu

1. The effects of strontium ions, Sr2+, on Ca(2+)-dependent feedback mechanisms during excitation-contraction coupling were examined in voltage-clamped rat ventricular myocytes in which intracellular [Ca2+] and [Sr2+] were monitored with the fluorescent indicator, indo-1. 2. Voltage clamp depolarizations and caffeine applications during superfusion in Ca(2+)-free, Sr(2+)-containing solutions were employed to exchange intracellular Ca2+ with Sr2+. Myocytes were loaded with Sr2+ by applying voltage clamp depolarizations during superfusion in Na(+)-free, Sr(2+)-containing solutions. 3. Caffeine applications produced large fluorescence transients in Sr(2+)-loaded cells. Thus, Sr2+ could be sequestered and released from the sarcoplasmic reticulum. 4. Ca2+ influx, but not Sr2+ influx, via sarcolemmal Ca2+ channels evoked ryanodine-sensitive fluorescence transients in Sr(2+)-loaded cells. These results demonstrated that Ca2+ influx-induced Sr2+ release (CISR) from the sarcoplasmic reticulum occurred in these experiments, even though Sr2+ influx-induced Sr2+ release was not observed. 5. The amplitude of the Ca2+ influx-induced fluorescence transient was 17 +/- 1% of the caffeine-induced transient (n = 5 cells), an indication that fractional utilization of Sr2+ sequestered in the sarcoplasmic reticulum during CISR was low. 6. With increased Sr2+ loading, the amplitude of Ca2+ influx- and caffeine-induced fluorescence transients increased, but fractional utilization of sarcoplasmic reticulum divalent cation stores was independent of the degree of Sr2+ loading. These data suggest that Ca2+ influx directly activated the release of divalent cations from the sarcoplasmic reticulum, but mechanisms promoting positive feedback of Sr2+ release were minimal during CISR. 7. By comparison, in Ca(2+)-loaded myocytes, Ca2+ influx-induced Ca2+ release (CICR) utilized a greater fraction of caffeine-releasable stores than CISR. Fractional utilization of Ca2+ stores during CICR increased with the degree of Ca2+ loading. 8. Taken together, these results suggest that Ca(2+)-dependent feedback mechanisms play a major role in determining the extent of sarcoplasmic reticulum Ca2+ release during cardiac excitation-contraction coupling under a wide range of conditions.

UI	MeSH Term	Description	Entries
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
D010726	Phosphodiesterase Inhibitors	Compounds which inhibit or antagonize the biosynthesis or actions of phosphodiesterases.	Phosphodiesterase Antagonists,Phosphodiesterase Inhibitor,Phosphoric Diester Hydrolase Inhibitors,Antiphosphodiesterases,Inhibitor, Phosphodiesterase
D002110	Caffeine	A methylxanthine naturally occurring in some beverages and also used as a pharmacological agent. Caffeine's most notable pharmacological effect is as a central nervous system stimulant, increasing alertness and producing agitation. It also relaxes SMOOTH MUSCLE, stimulates CARDIAC MUSCLE, stimulates DIURESIS, and appears to be useful in the treatment of some types of headache. Several cellular actions of caffeine have been observed, but it is not entirely clear how each contributes to its pharmacological profile. Among the most important are inhibition of cyclic nucleotide PHOSPHODIESTERASES, antagonism of ADENOSINE RECEPTORS, and modulation of intracellular calcium handling.	1,3,7-Trimethylxanthine,Caffedrine,Coffeinum N,Coffeinum Purrum,Dexitac,Durvitan,No Doz,Percoffedrinol N,Percutaféine,Quick-Pep,Vivarin,Quick Pep,QuickPep
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
D004558	Electric Stimulation	Use of electric potential or currents to elicit biological responses.	Stimulation, Electric,Electrical Stimulation,Electric Stimulations,Electrical Stimulations,Stimulation, Electrical,Stimulations, Electric,Stimulations, Electrical
D006352	Heart Ventricles	The lower right and left chambers of the heart. The right ventricle pumps venous BLOOD into the LUNGS and the left ventricle pumps oxygenated blood into the systemic arterial circulation.	Cardiac Ventricle,Cardiac Ventricles,Heart Ventricle,Left Ventricle,Right Ventricle,Left Ventricles,Right Ventricles,Ventricle, Cardiac,Ventricle, Heart,Ventricle, Left,Ventricle, Right,Ventricles, Cardiac,Ventricles, Heart,Ventricles, Left,Ventricles, Right
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
D012519	Sarcoplasmic Reticulum	A network of tubules and sacs in the cytoplasm of SKELETAL MUSCLE FIBERS that assist with muscle contraction and relaxation by releasing and storing calcium ions.	Reticulum, Sarcoplasmic,Reticulums, Sarcoplasmic,Sarcoplasmic Reticulums
D013324	Strontium	An element of the alkaline earth family of metals. It has the atomic symbol Sr, atomic number 38, and atomic weight 87.62.