Padjen A L, Smith P A
J Physiol. 1983 Mar;336:433-51. doi: 10.1113/jphysiol.1983.sp014589.
Drug responses of isolated hemisected frog spinal cords were examined by means of the sucrose-gap technique. The glutamate-induced depolarizations (glu-d) of motoneurones (recorded from ventral roots), and primary afferents (recorded from dorsal roots), were followed by an afterhyperpolarization (glu-a.h.). The depolarization induced by DL-homocysteic acid (DLH) was only occasionally followed by an afterhyperpolarization (DLH-a.h.). The glu-a.h. on both roots persisted in the presence of tetrodotoxin (TTX, 0.1-1 microM), or Ringer solution containing 10 mM-Mg2+; 0.1 mM-Ca2+ or 2 mM-Mn2+; 0.2 mM-Ca2+. This indicated that the response was neither due to the release of endogenous neurally active substances nor to the activation of a Ca2+-sensitive K+ conductance. The glu-a.h. was reduced or blocked by K+-free Ringer solution, 3-acetylstrophanthin (3-Ac-Str; 1 microM) or Li+ ions, and was therefore attributed to the activity of the electrogenic Na+ pump. The duration of depolarization induced by glu or DLH was increased in the presence of K+-free Ringer solution, 1 microM 3-Ac-Str or Li ions. It is therefore suggested that the electrogenic Na+ pump may play a role in limiting the duration of depolarization induced by the action of excitatory amino acids. The re-admission of K+ ions to preparations which had been incubated in K+-free Ringer solution produced a transient hyperpolarization (K-a.h.) of the membrane potential of ventral roots which is also attributable to the activation of the electrogenic Na+ pump. Both the K-a.h. and the glu-a.h. were enhanced in Ca2+-free Ringer solution. It is therefore suggested that the Ca2+ ions may modulate the activity of the electrogenic pump in central nervous tissue.
采用蔗糖间隙技术研究了离体半切青蛙脊髓的药物反应。谷氨酸诱导的运动神经元（从腹根记录）和初级传入神经元（从背根记录）的去极化（glu-d）之后会出现一个超极化后电位（glu-a.h.）。DL-高半胱氨酸（DLH）诱导的去极化偶尔会伴随一个超极化后电位（DLH-a.h.）。在存在河豚毒素（TTX，0.1 - 1 microM）或含有10 mM - Mg2+、0.1 mM - Ca2+或2 mM - Mn2+、0.2 mM - Ca2+的林格溶液时，两根神经上的glu-a.h.均持续存在。这表明该反应既不是由于内源性神经活性物质的释放，也不是由于对Ca2+敏感的K+电导的激活。glu-a.h.在无K+的林格溶液、3 - 乙酰毒毛旋花子苷（3 - Ac - Str；1 microM）或Li+离子存在时会减弱或被阻断，因此归因于电生性Na+泵的活性。在无K+的林格溶液、1 microM 3 - Ac - Str或Li离子存在时，谷氨酸或DLH诱导的去极化持续时间增加。因此提示电生性Na+泵可能在限制兴奋性氨基酸作用诱导的去极化持续时间中起作用。将在无K+的林格溶液中孵育过的标本重新加入K+离子会使腹根膜电位产生一个短暂的超极化（K - a.h.），这也归因于电生性Na+泵的激活。K - a.h.和glu-a.h.在无Ca2+的林格溶液中均增强。因此提示Ca2+离子可能调节中枢神经组织中电生性泵的活性。
