Sheridan R E, Deshpande S S, Lebeda F J, Adler M
Neurotoxicology Branch, United States Army Medical Research Institute of Chemical Defense, Aberdeen Proving Ground, MD 21010.
Brain Res. 1991 Aug 9;556(1):53-60. doi: 10.1016/0006-8993(91)90546-8.
The actions of pumiliotoxin-B, extracted from the skin of the frog Dendrobates pumilio, were examined on hippocampal slices and on acutely dissociated hippocampal neurons from the adult guinea pig. Application of 0.5-1 microM pumiliotoxin-B to hippocampal slices caused spontaneous, repetitive field discharges in the CA3 subfield. In whole-cell patch-clamp recordings of isolated CA1 and CA3 neurons, 1-2 microM pumiliotoxin-B shifted the midpoint of Na+ current activation by -11.4 +/- 1.1 mV. This shift was not dependent upon prior activation of the sodium channel. Pumiliotoxin-B did not block macroscopic Na+ inactivation but did reduce the apparent voltage-dependence of inactivation such that currents decayed faster at membrane potentials more negative than -30 mV. Single-channel recordings of sodium currents from excised membrane patches indicated that pumiliotoxin-B had little or no effect on channel closings due to entry into inactivated state(s) but did increase the rate of channel closings due to reversal of channel opening. The increase in the channel closing rate was consistent with a +8.7 mV shift in voltage sensitivity. Negative shifts in activation and positive shifts in closing rates implied a negative shift in the voltage-dependence of channel opening, suggesting that pumiliotoxin-B increases the rate of Na+ channel opening and closing in cells at rest, which could result in spontaneous activity in the neurons.
对从箭毒蛙皮肤中提取的蟾毒素 - B在成年豚鼠海马切片和急性分离的海马神经元上的作用进行了研究。将0.5 - 1微摩尔的蟾毒素 - B施加于海马切片，可在CA3亚区引起自发的、重复性的场电位发放。在分离的CA1和CA3神经元的全细胞膜片钳记录中，1 - 2微摩尔的蟾毒素 - B使Na⁺电流激活的中点负移了11.4±1.1毫伏。这种移位不依赖于钠通道的预先激活。蟾毒素 - B并不阻断宏观的Na⁺失活，但确实降低了失活的表观电压依赖性，使得电流在膜电位比 - 30毫伏更负时衰减得更快。从切除的膜片上记录的钠电流单通道记录表明，蟾毒素 - B对因进入失活状态而导致的通道关闭几乎没有影响，但确实增加了因通道开放逆转而导致的通道关闭速率。通道关闭速率的增加与电压敏感性正移8.7毫伏一致。激活的负移和关闭速率的正移意味着通道开放电压依赖性的负移，表明蟾毒素 - B增加了静息细胞中Na⁺通道的开放和关闭速率，这可能导致神经元的自发活动。
