Evidence for Na+/Ca2+ exchange in isolated smooth muscle cells: a fura-2 study |
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Authors: | Kevin Pritchard C C Ashley |
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Institution: | (1) University Laboratory of Physiology, Parks Road, OX1 3PT Oxford, UK;(2) The Cardiothoracic Institute, 2 Beaumont Street, W1N 2DX London, UK |
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Abstract: | Isolated smooth muscle cells (SMC) from guinea pig taenia coli were employed. Suspension of cells were externally loaded in saline with the fluorescent calcium indicators quin-2/AM or fura-2/AM at 20–40 M or 4 M respectively, resulting in an estimated intracellular concentration of 100–200 M for quin-2 or 10–20 M fura-2 (free acid). On addition of 100 M carbachol or high K
o
+
(80 mM) depolarization, fura-2 loaded cells contracted (104±47 m,n=121 rest: 39±13 m,n=59 contracted) identically to control (103±35 m,n=232 rest: 39±16 m,n=89 contracted) cells, whereas quin-2 loaded cells were unresponsive to these protocols and there was no significant length change. The Ca
i
2+
of fura-2 loaded cells was 100±18 nM (mean±SD,n=15) and was not significantly different from quin-2 loaded cells 107±26 nM (n=13). Treatment of fura-2 loaded cells with 100 M ouabain saline for 10–60 min progressively elevated the Ca
i
2+
to a mean of 266±83 nM (n=15). Reduction of Na
p
+
(96% Li+ replaced) significantly increased Ca
i
2+
to 317±77 nM (n=8). After pretreatment with ouabain (100 M), Na
o
+
replacement (Li+) increased Ca
i
2+
at a significantly faster rate 3.6 nM min–1 (control) cf. 19.8 nM min–1 (ouabain)]. |
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Keywords: | Fura-2 Na+/Ca2+ exchange Smooth muscle Ouabain |
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