Biomaterial Database

Divalent ion currents and the delayed potassium conductance in an Aplysia neurone. 1980

D J Adams, and P W Gage

1. In Na- and Ca-free external solutions, Sr or Ba (but not Mg) could act as carriers of inward current during action potentials in the neurone, R15 of the Aplysia abdominal ganglion. These action potentials exhibited a prolonged plateau phase, the duration of which was dependent on the concentration and species of divalent cation and activity of the neurone. 2. Depolarization of the soma membrane in Na-free Ba solution generated a prolonged, 'late' inward current the amplitude of which was dependent on the external Ba concentration. The Ba current was insensitive to tetrodotoxin but could be blocked by Mn2+ and Co2+ ions. 3. The peak current-voltage relation and threshold for activation of the late inward current was shifted to more negative potentials on replacement of Ca with Ba. The zero-current (reversal) potentials for both Sr and Ba were more negative than for Ca, indicating that the 'Ca' channel is less permeable to Sr2+ or Ba2+ ions than to Ca2+ ions. 4. Inactivation of the 'Ca' channel is slower in Ba than in Ca solution. The time course of Ba currents during a maintained depolarization of 2 sec could be reasonably described by the expression, I'Ba(t) = I'Ba (infinity) [1-exp(-t/tau M)]2exp(-t/tau H). 5. Time constants for activation (tau M) and inactivation (tau H) were voltage-dependent. In the range -10 to +30 mV, tau M varied from 15 to 5 msec and tau H from 2.0 to 0.5 sec (12 degrees C). Steady-state Ba conductance (corrected for inactivation) was voltage-dependent, increasing sigmoidally with depolarization to a maximum of approximately 12 microS at potentials beyond +15 mV. 6. Steady-state inactivation of Ba conductance (hBa(infinity)) varied with holding potential (VH). Conditioning holding potentials more negative than the resting potential (-40 to -50 mV) produced depression of Ba currents. Complete inactivation of Ba currents occurred at holding potentials more positive than 0 mV or with repetitive activation at frequencies greater than 1 Hz. 7. The divalent ions, Ba2+ and Sr2+, reversible depressed the total delayed K+ current at a rate dependent on the frequency of activation. Ba and Sr shifted the delayed K+ current-voltage curve to more positive voltages and depressed the delayed outward current at all membrane potentials. 8. Comparison of the effect of Ba on delayed K+ currents with those obtained in the presence of Mn2+ ions indicated that Ba2+ ions depress both the voltage-dependent and Ca-dependent components of the delayed K+ current. However, the mechanism by which Ba acts to inhibit the two components of the delayed K+ current appears to be different.

UI	MeSH Term	Description	Entries
D007473	Ion Channels	Gated, ion-selective glycoproteins that traverse membranes. The stimulus for ION CHANNEL GATING can be due to a variety of stimuli such as LIGANDS, a TRANSMEMBRANE POTENTIAL DIFFERENCE, mechanical deformation or through INTRACELLULAR SIGNALING PEPTIDES AND PROTEINS.	Membrane Channels,Ion Channel,Ionic Channel,Ionic Channels,Membrane Channel,Channel, Ion,Channel, Ionic,Channel, Membrane,Channels, Ion,Channels, Ionic,Channels, Membrane
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
D009474	Neurons	The basic cellular units of nervous tissue. Each neuron consists of a body, an axon, and dendrites. Their purpose is to receive, conduct, and transmit impulses in the NERVOUS SYSTEM.	Nerve Cells,Cell, Nerve,Cells, Nerve,Nerve Cell,Neuron
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.
D002413	Cations, Divalent	Positively charged atoms, radicals or groups of atoms with a valence of plus 2, which travel to the cathode or negative pole during electrolysis.	Divalent Cations
D004553	Electric Conductivity	The ability of a substrate to allow the passage of ELECTRONS.	Electrical Conductivity,Conductivity, Electric,Conductivity, Electrical
D005724	Ganglia	Clusters of multipolar neurons surrounded by a capsule of loosely organized CONNECTIVE TISSUE located outside the CENTRAL NERVOUS SYSTEM.
D000200	Action Potentials	Abrupt changes in the membrane potential that sweep along the CELL MEMBRANE of excitable cells in response to excitation stimuli.	Spike Potentials,Nerve Impulses,Action Potential,Impulse, Nerve,Impulses, Nerve,Nerve Impulse,Potential, Action,Potential, Spike,Potentials, Action,Potentials, Spike,Spike Potential
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
D001048	Aplysia	An opisthobranch mollusk of the order Anaspidea. It is used frequently in studies of nervous system development because of its large identifiable neurons. Aplysiatoxin and its derivatives are not biosynthesized by Aplysia, but acquired by ingestion of Lyngbya (seaweed) species.	Aplysias