Biomaterial Database

Membrane current and noise measurements in voltage-clamped node of Ranvier. 1980

R J van den Berg, and W H Rijnsburger

In voltage-clamp configurations for nodes of Ranvier the axoplasm resistance functions as a voltage-current converter. In existing configurations this resistance cannot be measured directly. In the present arrangement the electrical resistances of the preparation (axoplasm, membrane and seals) can be measured only from two measurements. This allows us to: 1. calibrate the ionic current under voltage-clamp conditions, and 2. calculate the intensity of the current fluctuations, not arising from the membrane (background noise). The measured axoplasm resistances are considerably higher than the values calculated on the basis of fiber geometry and axoplasm resistivity. The difference is due to the presence of constrictions in the nerve fiber. Membrane current estimation based on geometrical parameters in the presence of wide seals may contain large errors. Variations in the axoplasm resistance for voltage-membrane current conversion were observed within 1.5 hr. In 68% of the fibers this resistance decreased with 30% of the original value. With our current calibration the values for the maximum sodium conductance gNa (at 0mV membrane potential), maximum potassium conductance gK and leakage conductance gL are 49.5 X 10(-8), 6.66 X 10(-8) and 1.71 X 10(-8) S. respectively. The contribution of the different noise sources to the total background noise was calculated at the holding potential. For frequencies below 10(3) Hz there is an excellent agreement between measured and calculated noise levels.

UI	MeSH Term	Description	Entries
D008433	Mathematics	The deductive study of shape, quantity, and dependence. (From McGraw-Hill Dictionary of Scientific and Technical Terms, 6th ed)	Mathematic
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
D009412	Nerve Fibers	Slender processes of NEURONS, including the AXONS and their glial envelopes (MYELIN SHEATH). Nerve fibers conduct nerve impulses to and from the CENTRAL NERVOUS SYSTEM.	Cerebellar Mossy Fibers,Mossy Fibers, Cerebellar,Cerebellar Mossy Fiber,Mossy Fiber, Cerebellar,Nerve Fiber
D011893	Rana esculenta	An edible species of the family Ranidae, occurring in Europe and used extensively in biomedical research. Commonly referred to as "edible frog".	Pelophylax esculentus
D011901	Ranvier's Nodes	Regularly spaced gaps in the myelin sheaths of peripheral axons. Ranvier's nodes allow saltatory conduction, that is, jumping of impulses from node to node, which is faster and more energetically favorable than continuous conduction.	Nodes of Ranvier,Nodes, Ranvier's,Ranvier Nodes,Ranviers Nodes
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
D001370	Axonal Transport	The directed transport of ORGANELLES and molecules along nerve cell AXONS. Transport can be anterograde (from the cell body) or retrograde (toward the cell body). (Alberts et al., Molecular Biology of the Cell, 3d ed, pG3)	Axoplasmic Flow,Axoplasmic Transport,Axoplasmic Streaming,Axonal Transports,Axoplasmic Flows,Axoplasmic Transports,Streaming, Axoplasmic,Transport, Axonal,Transport, Axoplasmic,Transports, Axonal,Transports, Axoplasmic