Premium
Stimulation‐induced changes in [ca 2+ ] in lizard motor nerve terminals
Author(s) -
David Gavriel,
Barrett John N.,
Barrett Ellen F.
Publication year - 1997
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1111/j.1469-7793.1997.083bf.x
Subject(s) - stimulation , chemistry , bapta , biophysics , calcium , motor nerve , free nerve ending , anatomy , endocrinology , biology , organic chemistry
1 Motor axons were injected ionophoretically with one of five Ca 2+ ‐sensitive dyes (fluo‐3, Calcium Green‐2, Calcium Green‐5N, fluo‐3FF and Oregon Green BAPTA‐5N). Changes in fluorescence (Δ F/F rest ) within motor terminal boutons following a single action potential and brief stimulus trains were monitored with high temporal resolution using a confocal microscope. 2 Stimulation‐induced increases in Δ F/F rest were confined primarily to boutons, with roughly uniform increases in all the boutons of a terminal. The increase in Δ F/F rest began prior to, and decayed more slowly than, the endplate potential (EPP) recorded in the underlying muscle fibre. Δ F/F rest was graded with bath [Ca 2+ ]. Both Δ F/F rest and the EPP were reduced, but not eliminated, by ω‐conotoxin GVIA (5–10 μ m ). 3 For dyes with lower affinity for Ca 2+ (e.g. Oregon Green BAPTA‐5N, K d ≈ m m ) stimulation‐induced increases in Δ F/F rest were measured in the presence of the K + channel blocker 3,4‐diaminopyridine (3,4‐DAP, 100 m m ). During brief stimulus trains (4 at 50 Hz) in 3,4‐DAP, the EPP exhibited profound depression, but the fluorescence increase associated with each stimulus showed little decrement, suggesting that depression was not mediated by a reduction in Ca 2+ entry. 4 For dyes with a higher affinity for Ca 2+ (e.g. fluo‐3, K d ≈ 0.5–1 μ m ) stimulation‐induced increases in Δ F/F rest could also be measured in normal physiological saline. Increases in Δ F/F rest were much greater with 3,4‐DAP present, but the amplitude decreased with successive stimuli due to partial dye saturation. 5 Calculations suggested that following a single action potential the average [Ca 2+ ] within a bouton increased by up to 150 n m in normal saline and 940 nM in 3,4‐DAP. With low affinity dyes the Δ F/F rest measured near the membrane had a higher peak amplitude and a faster early decay than that measured in the centre of the bouton, suggesting that substantial spatial [Ca 2+ ] gradients exist within boutons for at least 15 ms following stimulation.