Gusovsky F, Nishizawa Y, Padgett W, McNeal E T, Rice K, Kim C H, Creveling C R, Daly J W
Laboratory of Bioorganic Chemistry, National Institute of Diabetes, Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892.
Brain Res. 1990 Jun 4;518(1-2):101-6. doi: 10.1016/0006-8993(90)90959-f.
22Na+ influx and binding of [3H]saxitoxin ([3H]STX) and [3H]batrachotoxin-A 20-alpha-benzoate ([3H]BTX-B) were studied in guinea pig cerebral synaptoneurosomes. STX and tetrodotoxin (TTX) completely blocked the stimulation of sodium influx induced by 1 microM BTX. The IC50 values for STX and TTX closely matched the Ki values for inhibition of [3H]STX binding, suggesting that the sites labelled by [3H]STX are associated with a population of BTX-sensitive channels. BTX induced a dose-dependent stimulation of sodium influx in synaptoneurosomes (EC50 280 nM). The potency of BTX for stimulation of sodium influx was increased (EC50 24 nM) in the presence of 0.6 microgram/ml scorpion venom without any change in maximal influx. In contrast, specific binding of [3H]BTX-B to synaptoneurosomes was minimal in the absence of scorpion venom, but it was increased several fold in the presence of 60 micrograms/ml scorpion venom. With proparacaine isothiocyanate (PROPRIT), an irreversible local anesthetic, the inhibition of [3H]BTX-B binding by PROPRIT did not occur in parallel with an inhibition of sodium influx induced by BTX. Preincubation of synaptoneurosomes with 10 microM PROPRIT for 10 min resulted in approximately 70% inhibition of [3H]BTX-B binding in the presence of scorpion venom. Such preincubation did not alter BTX-induced sodium uptake in synaptoneurosomes. Preincubations of synaptoneurosomes with 100 microM PROPRIT for 10 min completely inhibited [3H]BTX-B binding, and under these conditions BTX-induced sodium influx was reduced only by 50%. The results indicate that virtual elimination of binding sites labeled by [3H]BTX-B in the presence of scorpion venom by PROPRIT has little effect on sodium influx induced by BTX.(ABSTRACT TRUNCATED AT 250 WORDS)
在豚鼠脑突触神经小体中研究了22Na+内流以及[3H]石房蛤毒素（[3H]STX）和[3H]蛙毒素-A 20-α-苯甲酸酯（[3H]BTX-B）的结合情况。STX和河豚毒素（TTX）完全阻断了1 microM BTX诱导的钠内流刺激。STX和TTX的IC50值与抑制[3H]STX结合的Ki值紧密匹配，表明[3H]STX标记的位点与一群对BTX敏感的通道相关。BTX在突触神经小体中诱导了剂量依赖性的钠内流刺激（EC50为280 nM）。在存在0.6微克/毫升蝎毒的情况下，BTX刺激钠内流的效力增加（EC50为24 nM），而最大内流无任何变化。相反，在不存在蝎毒时，[3H]BTX-B与突触神经小体的特异性结合极少，但在存在60微克/毫升蝎毒时增加了几倍。对于不可逆局部麻醉药异硫氰酸丙氧卡因（PROPRIT），PROPRIT对[3H]BTX-B结合的抑制与BTX诱导的钠内流抑制并不平行。突触神经小体与10 microM PROPRIT预孵育10分钟，在存在蝎毒的情况下导致[3H]BTX-B结合约70%的抑制。这种预孵育并未改变BTX诱导的突触神经小体钠摄取。突触神经小体与100 microM PROPRIT预孵育10分钟完全抑制了[3H]BTX-B结合，在这些条件下，BTX诱导的钠内流仅减少50%。结果表明，在存在蝎毒的情况下PROPRIT几乎消除[3H]BTX-B标记的结合位点对BTX诱导的钠内流影响很小。（摘要截短于250字）
