Biomaterial Database

Calcium influx in resting conditions in a preparation of peptidergic nerve terminals isolated from the rat neurohypophysis. 1991

E C Toescu

Department of Human Anatomy, Oxford University.

1. Calcium accumulation in a preparation of nerve terminals isolated from the rat neurohypophysis was measured both in rapid (10-60 s) and long-term (up to 60 min) uptake experiments, by use of 45Ca2+ as radiotracer and ion-exchange chromatography as separation method. Unless otherwise stated all experiments have been performed in the absence from the incubation media of secretagogues or depolarizing agents. 2. The uptake of 45Ca2+ in nerve terminals was linear up to 30-45 s, with an apparent initial rate of uptake of 0.98 nmol Ca2+ (mg protein)-1 min-1. 3. The level of 45Ca2+ accumulation was sensitive to manipulations of electrochemical gradient for Na+ across the plasma membrane. Alterations of extracellular concentrations of Na+ affected secretory activity to a larger extent than manipulations of internal Na+. These effects were not qualitatively dependent on the nature of the replacement for Na+. 4. Removal of extracellular Na+ induced a significant increase of both the level of 45Ca2+ accumulation and of the apparent initial rate of uptake. The concentration for half-maximal stimulatory effect was 40 mM-Na+. 5. The analysis of the stimulatory effect of high extracellular K+ on the 45Ca2+ accumulation reveals at least two components: a depolarization and an intrinsic K+ effect. 6. Sodium channel inhibitors (TTX, 1.25 microM) decreased significantly the level of 45Ca2+ accumulation, an effect which was evident from the first minute of exposure to the drug. 7. A specific L-type Ca2+ channel blocker (nicardipine) inhibited 45Ca2+ uptake, in a dose-dependent manner. Simultaneous addition of both TTX and nicardipine (20 microM) decreases the 45Ca2+ uptake up to 50%. 8. In conclusion, the uptake of Ca2+ in isolated peptidergic nerve terminals, incubated in resting conditions, is mediated by at least three pathways: a TTX-sensitive and a nicardipine (dihydropyrine)-sensitive pathway and through a Na(+)-Ca2+ exchange-dependent mechanism. The principal route of Ca2+ entry appears to be through TTX-sensitive channels.

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
D009411	Nerve Endings	Branch-like terminations of NERVE FIBERS, sensory or motor NEURONS. Endings of sensory neurons are the beginnings of afferent pathway to the CENTRAL NERVOUS SYSTEM. Endings of motor neurons are the terminals of axons at the muscle cells. Nerve endings which release neurotransmitters are called PRESYNAPTIC TERMINALS.	Ending, Nerve,Endings, Nerve,Nerve Ending
D009529	Nicardipine	A potent calcium channel blockader with marked vasodilator action. It has antihypertensive properties and is effective in the treatment of angina and coronary spasms without showing cardiodepressant effects. It has also been used in the treatment of asthma and enhances the action of specific antineoplastic agents.	Antagonil,Cardene,Cardene I.V.,Cardene SR,Dagan,Flusemide,Lecibral,Lincil,Loxen,Lucenfal,Nicardipine Hydrochloride,Nicardipine LA,Nicardipino Ratiopharm,Nicardipino Seid,Perdipine,Ridene,Vasonase,Y-93,Hydrochloride, Nicardipine,LA, Nicardipine,Y 93,Y93
D010904	Pituitary Gland, Posterior	Neural tissue of the pituitary gland, also known as the neurohypophysis. It consists of the distal AXONS of neurons that produce VASOPRESSIN and OXYTOCIN in the SUPRAOPTIC NUCLEUS and the PARAVENTRICULAR NUCLEUS. These axons travel down through the MEDIAN EMINENCE, the hypothalamic infundibulum of the PITUITARY STALK, to the posterior lobe of the pituitary gland.	Neurohypophysis,Infundibular Process,Lobus Nervosus,Neural Lobe,Pars Nervosa of Pituitary,Posterior Lobe of Pituitary,Gland, Posterior Pituitary,Infundibular Processes,Lobe, Neural,Lobes, Neural,Nervosus, Lobus,Neural Lobes,Pituitary Pars Nervosa,Pituitary Posterior Lobe,Posterior Pituitary Gland,Posterior Pituitary Glands,Process, Infundibular,Processes, Infundibular
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
D002462	Cell Membrane	The lipid- and protein-containing, selectively permeable membrane that surrounds the cytoplasm in prokaryotic and eukaryotic cells.	Plasma Membrane,Cytoplasmic Membrane,Cell Membranes,Cytoplasmic Membranes,Membrane, Cell,Membrane, Cytoplasmic,Membrane, Plasma,Membranes, Cell,Membranes, Cytoplasmic,Membranes, Plasma,Plasma Membranes
D000494	Allosteric Regulation	The modification of the reactivity of ENZYMES by the binding of effectors to sites (ALLOSTERIC SITES) on the enzymes other than the substrate BINDING SITES.	Regulation, Allosteric,Allosteric Regulations,Regulations, Allosteric
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