CALCIUM INFLUX IN INTERNALLY DIALYZED SQUID GIANT-AXONS
CALCIUM INFLUX IN INTERNALLY DIALYZED SQUID GIANT-AXONS
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DOI：
10.1085/jgp.73.1.91
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发表时间：
1979-01-01
影响因子：
3.8
通讯作者：
DIPOLO, R
中科院分区：
文献类型：
--
作者：
DIPOLO, R
A method was developed to measure Ca influx in internally dialyzed squid [Doryteuthis plei] axons. This was achieved by controlling the dialyzed segment of the axon exposed to the external radioactive medium. The capacity of EGTA [ethyleneglycol-bis (.beta. aminoethyl ether) N,N,N'',N''-tetraacetic acid] to buffer all the Ca entering the fiber was explored by changing the free EGTA at constant inside concentration, [Ca2+]i. At a free [EGTA]i > 200 .mu.M, the measured resting Ca influx and the expected increment in Ca entry during electrical stimulation were independent of the axoplasmic free [EGTA]. To avoid Ca uptake by the mitochondrial system, cyanide, oligomycin and FCCP [carbonylcyanide-p-trifluoro-methoxyphenylhydrazone] were included in the perfusate. Axons dialyzed with a standard medium ([ATP] = 2 mM, [Ca2+]i = 0.06 .mu.M, outside concentration [Ca2+]o = 10 mM, [Na+]i = 70 mM and [Na+]o = 465 mM) gave a mean Ca influx of 0.14 .+-. 0.012 pmol .cntdot. cm-2 .cntdot. s-1 (n = 12). Removal of ATP decreased the Ca influx to 0.085 .+-. 0.007 pmol .cntdot. cm-2 .cntdot. s-1 (n =12). Ca influx increased to 0.35 pmol .cntdot. cm-2 .cntdot. s-1 when Nao was removed. This increment was completely abolished by removing Nai+ and/or ATP from the dialysis medium. At nominal zero [Ca2+]i, no Nai-dependent Ca influx was observed. In the presence of ATP and Nai, [Ca2+]i, activated the Ca influx along a sigmoid curve without saturation up to 1 .mu.M [Ca2+]i. Removal of Nai+ always reduced the Ca influx to a value similar to that observed in the absence of [Ca2+]i (0.087 .+-. 0.008 pmol .cntdot. cm-2 .cntdot. s-1; n = 11). Under these standard conditions, 50-60% of the total Ca influx was insensitive to Nai+ Cai2+ and ATP, sensitive to membrane potential and partially inhibited by external Co2+.
