Neuroscience 2004 Abstract
| Presentation Number: | 513.20 |
|---|---|
| Abstract Title: | Extracellular diffusion of divalent anions and cations in rat hippocampus exhibits charge-based discrimination. |
| Authors: |
Hrabetova, S.*1
; Nicholson, C.1
1Dept. of Physiology & Neurosci., NYU Sch. of Med., New York, NY |
| Primary Theme and Topics |
Synaptic Transmission and Excitability - Synaptic Plasticity -- Other |
| Session: |
513. Synaptic Plasticity: Short-Term Plasticity and Physiology Poster |
| Presentation Time: | Monday, October 25, 2004 4:00 PM-5:00 PM |
| Location: | San Diego Convention Center - Hall A-H, Board # L13 |
| Keywords: | TORTUOSITY, LUCIFER YELLOW, CALCIUM, EXTRACELLULAR MATRIX |
Extracellular transport of molecules is slowed down by tissue hindrance that is defined by the tortuosity, λ = (D/D*)0.5, where D is the free diffusion coefficient and D* is the effective diffusion coefficient in tissue (Nicholson 2001, Rep Prog Phys 64:815). In cartilage or capillary glycocalyx, there is a pronounced charge-based interaction between transported molecules and the extracellular environment, manifested in λ (Maroudas 1970, Biophys J 10:365; Stace & Damiano 2001, Biophys J 80:1670). In cerebellum, however, monovalent anions and cations are hindered equally (Nicholson & Phillips 1981, J Physiol 321:225). We recently found that λ measured in the stratum radiatum of hippocampal CA1 region with tetramethylammonium (TMA+, MW 74) was 1.47 but only 1.29 when divalent anion Lucifer Yellow (LY2-, MW 457) was employed (Hrabetova et al. 2003, SFN Program No. 477.8). We hypothesize that the transport of divalent, but not monovalent, ions in brain is governed by charge-based discrimination. To test this we measured the diffusion of monovalent anion, α-naphthalenesulphonate (α-NS-, MW 207), and divalent cation, Ca2+ (MW 40), in rat hippocampal slices (400 μm). Ions were delivered by a pressure pulse applied to a micropipette in the stratum radiatum and detected with ion-selective microelectrodes sensing α-NS- or Ca2+ placed 100-150 μm away (Nicholson & Rice 1987, Can J Physiol Pharmacol 65:1086). At 34°C, α-NS- and Ca2+ moved with D* = 3.1 ± 0.2 × 10-6 cm2s-1 (mean ± SD, n = 4) and 2.1 ± 0.3 × 10-6 cm2s-1 (n = 32), respectively. Based on the free diffusion coefficients [Dα-NS = 7.1 ± 0.3 × 10-6 cm2s-1 (n = 13) and DCa = 9.4 ± 1.3 × 10-6 cm2s-1 (n = 22)] measured at 34°C in 0.3% agarose gel, λα-NS = 1.51 and λCa = 2.1. In summary, λLY < λα-NS ≌ λTMA < λCa. We speculate that low λLY and high λCa reflect the interaction of divalent ions with negative charges on the extracellular matrix.
Supported by NIH Grant NS 28642
Sample Citation:
[Authors]. [Abstract Title]. Program No. XXX.XX. 2004 Neuroscience Meeting Planner. San Diego, CA: Society for Neuroscience, 2004. Online.
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