Neurotransmitters can effect cell function by binding to receptors associated with ion channels (ionotropic receptors) or to receptors that stimulate second messenger production (metabotropic receptors). The gating of ion channels results in changes in membrane potential that alters cell excitability. Second messengers often bring about an increase in intracellular Ca2+. Cytoplasmic Ca2+ transients trigger key cellular events including modification of excitability, cell growth and transmitter release. The long-term objective of the proposed research is to understand the mechanisms of action of neurotransmitters on ion permeation and Ca2+ metabolism in fish retinal horizontal cells.
The specific aims are to determine the basic mechanisms of ion permeation initiated through ligand gated channels, the functional components of the proteins that constitute these channels, the changes in intracellular Ca2+ initiated by neurotransmitters that may be important in regulating the electrical activity of horizontal cells and the neurotoxic response. Two approaches will be used. One employs whole cell voltage clamp using patch electrodes to measure the membrane current produced by applied neurotransmitters and pharmacological agents that modify either the action of the transmitters or the amino acid composition of the receptor/channel protein. The second method will utilize the Ca2+ sensitive fluorescent indicator fura-2 to measure intracellular Ca2+ concentration in the presence of neurotransmitters. These experiments will be done on voltage clamped cells so as to distinguish the contributions to the changes in intracellular Ca2+ made by voltage sensitive Ca2+ channels and ligand gated channels. To carry out these studies, a concentration clamp system has been developed that permits the rapid exchange of solutions while maintaining the cell under voltage clamp with simultaneous measurement of cell fluorescence. Under these conditions, precise control of known concentrations of drugs is maintained. The measure of cell viability as a function of [Ca2+]i will be determined by cell shape and cell response to agonists or changes in membrane voltage. The results from this research will provide new and extensive information on many of the structural and biophysical properties of neurotransmitter- receptor interactions. The results of this investigation will have health- related implications since neurons rely on interactions with chemical reagents for several key functions.

Agency
National Institute of Health (NIH)
Institute
National Eye Institute (NEI)
Type
Research Project (R01)
Project #
5R01EY001897-15
Application #
3256305
Study Section
Visual Sciences A Study Section (VISA)
Project Start
1978-05-01
Project End
1995-09-29
Budget Start
1992-09-30
Budget End
1993-09-29
Support Year
15
Fiscal Year
1992
Total Cost
Indirect Cost
Name
University of Texas Medical Br Galveston
Department
Type
Schools of Medicine
DUNS #
041367053
City
Galveston
State
TX
Country
United States
Zip Code
77555
Micci, M A; Christensen, B N (1996) Distribution of the inositol trisphosphate receptor in the catfish retina. Brain Res 720:139-47
Linn, C P; Christensen, B N (1992) Excitatory amino acid regulation of intracellular Ca2+ in isolated catfish cone horizontal cells measured under voltage- and concentration-clamp conditions. J Neurosci 12:2156-64
O'Dell, T J; Christensen, B N (1989) A voltage-clamp study of isolated stingray horizontal cell non-NMDA excitatory amino acid receptors. J Neurophysiol 61:162-72
O'Dell, T J; Christensen, B N (1989) Horizontal cells isolated from catfish retina contain two types of excitatory amino acid receptors. J Neurophysiol 61:1097-109
O'Dell, T J; Christensen, B N (1988) Mecamylamine is a selective non-competitive antagonist of N-methyl-D-aspartate- and aspartate-induced currents in horizontal cells dissociated from the catfish retina. Neurosci Lett 94:93-8
Sakuranaga, M; Ando, Y; Naka, K (1987) Dynamics of the ganglion cell response in the catfish and frog retinas. J Gen Physiol 90:229-59
Hals, G; Christensen, B N; O'Dell, T et al. (1986) Voltage-clamp analysis of currents produced by glutamate and some glutamate analogues on horizontal cells isolated from the catfish retina. J Neurophysiol 56:19-31
Hidaka, S; Christensen, B N; Naka, K (1986) The synaptic ultrastructure in the outer plexiform layer of the catfish retina: a three-dimensional study with HVEM and conventional EM of Golgi-impregnated bipolar and horizontal cells. J Comp Neurol 247:181-99
O'Dell, T; Christensen, B N (1986) N-methyl-D-aspartate receptors coexist with kainate and quisqualate receptors on single isolated catfish horizontal cells. Brain Res 381:359-62
Sakuranaga, M; Sato, S; Hida, E et al. (1986) Nonlinear analysis: mathematical theory and biological applications. Crit Rev Biomed Eng 14:127-84

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