Biomaterial Database

Na+ currents through low-voltage-activated Ca2+ channels of chick sensory neurones: block by external Ca2+ and Mg2+. 1990

H D Lux, and E Carbone, and H Zucker

Department of Neurophysiology, Max-Planck-Institute for Psychiatry, Planegg, FRG.

1. Whole-cell currents through low-voltage-activated (LVA) Ca2+ channels carried by monovalent cations were studied in chick dorsal root ganglion (DRG) cells. 2. With 120 mM [Na+] on both sides of the membrane and [Ca2+]o less than or equal to 100 microM, the currents reversed at 0 mV. Their half-times of activation and inactivation were strictly voltage-dependent and decreased to near-constant values of 0.6-0.85 and 40 ms, respectively, at positive membrane potentials. The longer activation times were observed with [Ca2+]o greater than or equal to 50 microM. 3. The selectivity of the Ca2+ channel for monovalent ions with reference to internal Na+ was evaluated from the reversal potential. The Li+ and Na+ permeabilities were similar. The permeability ratios of K+ and Rb+ were 0.45, and 0.33 for Cs+. 4. Micromolar increases in [Ca2+]o produced small voltage shifts of half-times of activation (less than or equal to +3 mV at 10 microM and +10 mV at 500 microM), but strongly depressed the Na+ current. The Ca2(+)-induced block of Na+ current satisfied a 1:1 stoichiometry with an apparent KD of 1.8 microM at -20 mV. The block was, however, relieved with more positive and negative potentials, with KDs of 55 and 8.5 microM at +90 and -110 mV, respectively. 5. Relaxation time constants of block and unblock of Na+ currents through the LVA Ca2+ channel were measured on step changes to and from membrane potentials at which pronounced Ca2(+)-induced block occurred. 6. At -20 mV, the time constants of block decreased with micromolar increase in [Ca2+]o in line with a blocking rate coefficient of 1.9 x 10(8) M-1 s-1, but settled to values of 0.18 ms at [Ca2+]o beyond 50 microM. The Na+ currents were unblocked with time constant (tau u) of around 0.25 ms at strongly positive and negative membrane potentials at 22 degrees C. 7. Tau u failed to show any obvious dependence on [Ca2+]o up to the millimolar range. This finding contradicts suggestions that removal of the block occurs in a [Ca2+]o-dependent manner as a result of an increased probability of Ca2+ ion mobilization by repulsive forces with increased Ca2+ occupation of the channel. 8. The time course of unblock of Na+ currents was strongly temperature-dependent showing a Q10 of 2.5 for tau u. 9. The voltage dependence of the Na+ current block by Ca2+ ions is best accounted for by a single, centrally located Ca2+ binding site.(ABSTRACT TRUNCATED AT 400 WORDS)

UI	MeSH Term	Description	Entries
D007700	Kinetics	The rate dynamics in chemical or physical systems.
D008274	Magnesium	A metallic element that has the atomic symbol Mg, atomic number 12, and atomic weight 24.31. It is important for the activity of many enzymes, especially those involved in OXIDATIVE PHOSPHORYLATION.
D009475	Neurons, Afferent	Neurons which conduct NERVE IMPULSES to the CENTRAL NERVOUS SYSTEM.	Afferent Neurons,Afferent Neuron,Neuron, Afferent
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
D002478	Cells, Cultured	Cells propagated in vitro in special media conducive to their growth. Cultured cells are used to study developmental, morphologic, metabolic, physiologic, and genetic processes, among others.	Cultured Cells,Cell, Cultured,Cultured Cell
D002642	Chick Embryo	The developmental entity of a fertilized chicken egg (ZYGOTE). The developmental process begins about 24 h before the egg is laid at the BLASTODISC, a small whitish spot on the surface of the EGG YOLK. After 21 days of incubation, the embryo is fully developed before hatching.	Embryo, Chick,Chick Embryos,Embryos, Chick
D005727	Ganglia, Spinal	Sensory ganglia located on the dorsal spinal roots within the vertebral column. The spinal ganglion cells are pseudounipolar. The single primary branch bifurcates sending a peripheral process to carry sensory information from the periphery and a central branch which relays that information to the spinal cord or brain.	Dorsal Root Ganglia,Spinal Ganglia,Dorsal Root Ganglion,Ganglion, Spinal,Ganglia, Dorsal Root,Ganglion, Dorsal Root,Spinal Ganglion
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
D013696	Temperature	The property of objects that determines the direction of heat flow when they are placed in direct thermal contact. The temperature is the energy of microscopic motions (vibrational and translational) of the particles of atoms.	Temperatures