Biomaterial Database

Two components of calcium currents in the soma of photoreceptors of Hermissenda. 1994

E N Yamoah, and T Crow

Department of Neurobiology and Anatomy, University of Texas, Medical School, Houston 77030.

1. The proposed mechanism of cellular plasticity underlying classical conditioning of Hermissenda involves Ca2+ influx through voltage-activated channels. This influx triggers several molecular cascades and leads to the phosphorylation of K+ channels in identified photoreceptors. We studied Ca2+ currents from isolated photoreceptors of Hermissenda with the whole cell patch-clamp technique. Two distinct Ca2+ currents were identified in isolated photoreceptors on the basis of differences in their voltage dependence, kinetics, and pharmacology. 2. One Ca2+ current was transient (ICa(t)), with a fast onset (approximately 5 ms), activated at -50 mV from a holding potential of -90 mV, and peaked at 0 mV. The second Ca2+ current, designated as sustained (ICa(s)), exhibited a delayed time-to-peak, activated at -30 mV, and reached maximum at 30 mV. 3. Steady-state activation curves for both currents were generated from normalized currents and fitted with the Boltzmann function; estimates of half-activation voltages for ICa(t) were -38.8 +/- 6.7 mV (mean +/- SD; n = 9) and 3.2 +/- 8.2 mV for ICa(s) (n = 11) with maximum slopes of 8.9 +/- 1.6 mV (n = 9) and 11.0 +/- 2.4 mV (n = 11). 4. The inactivation of ICa(s) was slow (time constants > 3 s) whereas ICa(t) inactivated rapidly (time constant of inactivation at various voltages; 75-600 ms). 5. Ni2+ (0.8 mM), Gd3+ (0.5 mM), and amiloride (10 microM) produced a reversible block of ICa(t) without affecting ICa(s). omega-Conotoxin GVIA (10 nM) irreversibly blocked ICa(s) whereas nitrendipine (20 microM) produced a reversible block. 6. ICa(t) may be responsible for steady-state membrane potential oscillations. ICa(s) may contribute to the maintenance of the amplitude of the plateau phase of the generator potential.

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
D009435	Synaptic Transmission	The communication from a NEURON to a target (neuron, muscle, or secretory cell) across a SYNAPSE. In chemical synaptic transmission, the presynaptic neuron releases a NEUROTRANSMITTER that diffuses across the synaptic cleft and binds to specific synaptic receptors, activating them. The activated receptors modulate specific ion channels and/or second-messenger systems in the postsynaptic cell. In electrical synaptic transmission, electrical signals are communicated as an ionic current flow across ELECTRICAL SYNAPSES.	Neural Transmission,Neurotransmission,Transmission, Neural,Transmission, Synaptic
D009473	Neuronal Plasticity	The capacity of the NERVOUS SYSTEM to change its reactivity as the result of successive activations.	Brain Plasticity,Plasticity, Neuronal,Axon Pruning,Axonal Pruning,Dendrite Arborization,Dendrite Pruning,Dendritic Arborization,Dendritic Pruning,Dendritic Remodeling,Neural Plasticity,Neurite Pruning,Neuronal Arborization,Neuronal Network Remodeling,Neuronal Pruning,Neuronal Remodeling,Neuroplasticity,Synaptic Plasticity,Synaptic Pruning,Arborization, Dendrite,Arborization, Dendritic,Arborization, Neuronal,Arborizations, Dendrite,Arborizations, Dendritic,Arborizations, Neuronal,Axon Prunings,Axonal Prunings,Brain Plasticities,Dendrite Arborizations,Dendrite Prunings,Dendritic Arborizations,Dendritic Prunings,Dendritic Remodelings,Network Remodeling, Neuronal,Network Remodelings, Neuronal,Neural Plasticities,Neurite Prunings,Neuronal Arborizations,Neuronal Network Remodelings,Neuronal Plasticities,Neuronal Prunings,Neuronal Remodelings,Neuroplasticities,Plasticities, Brain,Plasticities, Neural,Plasticities, Neuronal,Plasticities, Synaptic,Plasticity, Brain,Plasticity, Neural,Plasticity, Synaptic,Pruning, Axon,Pruning, Axonal,Pruning, Dendrite,Pruning, Dendritic,Pruning, Neurite,Pruning, Neuronal,Pruning, Synaptic,Prunings, Axon,Prunings, Axonal,Prunings, Dendrite,Prunings, Dendritic,Prunings, Neurite,Prunings, Neuronal,Prunings, Synaptic,Remodeling, Dendritic,Remodeling, Neuronal,Remodeling, Neuronal Network,Remodelings, Dendritic,Remodelings, Neuronal,Remodelings, Neuronal Network,Synaptic Plasticities,Synaptic Prunings
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
D003214	Conditioning, Classical	Learning that takes place when a conditioned stimulus is paired with an unconditioned stimulus.	Reflex, Conditioned,Classical Conditioning,Classical Conditionings,Conditioned Reflex,Conditionings, Classical
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
D012908	Snails	Marine, freshwater, or terrestrial mollusks of the class Gastropoda. Most have an enclosing spiral shell, and several genera harbor parasites pathogenic to man.	Snail
D015220	Calcium Channels	Voltage-dependent cell membrane glycoproteins selectively permeable to calcium ions. They are categorized as L-, T-, N-, P-, Q-, and R-types based on the activation and inactivation kinetics, ion specificity, and sensitivity to drugs and toxins. The L- and T-types are present throughout the cardiovascular and central nervous systems and the N-, P-, Q-, & R-types are located in neuronal tissue.	Ion Channels, Calcium,Receptors, Calcium Channel Blocker,Voltage-Dependent Calcium Channel,Calcium Channel,Calcium Channel Antagonist Receptor,Calcium Channel Antagonist Receptors,Calcium Channel Blocker Receptor,Calcium Channel Blocker Receptors,Ion Channel, Calcium,Receptors, Calcium Channel Antagonist,VDCC,Voltage-Dependent Calcium Channels,Calcium Channel, Voltage-Dependent,Calcium Channels, Voltage-Dependent,Calcium Ion Channel,Calcium Ion Channels,Channel, Voltage-Dependent Calcium,Channels, Voltage-Dependent Calcium,Voltage Dependent Calcium Channel,Voltage Dependent Calcium Channels
D015221	Potassium Channels	Cell membrane glycoproteins that are selectively permeable to potassium ions. At least eight major groups of K channels exist and they are made up of dozens of different subunits.	Ion Channels, Potassium,Ion Channel, Potassium,Potassium Channel,Potassium Ion Channels,Channel, Potassium,Channel, Potassium Ion,Channels, Potassium,Channels, Potassium Ion,Potassium Ion Channel
D015398	Signal Transduction	The intracellular transfer of information (biological activation/inhibition) through a signal pathway. In each signal transduction system, an activation/inhibition signal from a biologically active molecule (hormone, neurotransmitter) is mediated via the coupling of a receptor/enzyme to a second messenger system or to an ion channel. Signal transduction plays an important role in activating cellular functions, cell differentiation, and cell proliferation. Examples of signal transduction systems are the GAMMA-AMINOBUTYRIC ACID-postsynaptic receptor-calcium ion channel system, the receptor-mediated T-cell activation pathway, and the receptor-mediated activation of phospholipases. Those coupled to membrane depolarization or intracellular release of calcium include the receptor-mediated activation of cytotoxic functions in granulocytes and the synaptic potentiation of protein kinase activation. Some signal transduction pathways may be part of larger signal transduction pathways; for example, protein kinase activation is part of the platelet activation signal pathway.	Cell Signaling,Receptor-Mediated Signal Transduction,Signal Pathways,Receptor Mediated Signal Transduction,Signal Transduction Pathways,Signal Transduction Systems,Pathway, Signal,Pathway, Signal Transduction,Pathways, Signal,Pathways, Signal Transduction,Receptor-Mediated Signal Transductions,Signal Pathway,Signal Transduction Pathway,Signal Transduction System,Signal Transduction, Receptor-Mediated,Signal Transductions,Signal Transductions, Receptor-Mediated,System, Signal Transduction,Systems, Signal Transduction,Transduction, Signal,Transductions, Signal