AN EXAMINATION OF EFFECTS OF OSMOTIC PRESSURE CHANGES UPON TRANSMITTER RELEASE FROM MAMMALIAN MOTOR NERVE TERMINALS
AN EXAMINATION OF EFFECTS OF OSMOTIC PRESSURE CHANGES UPON TRANSMITTER RELEASE FROM MAMMALIAN MOTOR NERVE TERMINALS
复制标题
DOI：
10.1113/jphysiol.1968.sp008579
复制
发表时间：
1968-01-01
影响因子：
5.5
通讯作者：
LANDAU, EM
中科院分区：
文献类型：
--
作者：
HUBBARD, JI;JONES, SF;LANDAU, EM
在渗透压为200~700m-moles/l的溶液中，测定大鼠离体膈神经肌肉接头处的微型终板电位(MEPP)频率时，渗透梯度超过75m-moles/l时，MEPP频率一过性增加，然后在1小时内下降。要稳定到略高于频率控制水平的水平。较小的渗透梯度导致MEPP频率持续增加。当制剂暴露在渗透压为500或600m-osmoles/L的溶液中时，EPP量子含量最初增加，后来显著降低，但不受较低高渗溶液的影响。浴液中钙或镁含量的变化不改变渗透压对MEPP频率或EPP量子含量的早期瞬时增加的影响，但影响后期MEPP频率的稳定增加。MEPP频率的瞬时增高值与渗透梯度在0-300m-osmoles/1范围内呈指数关系，qio为1.95(IL-34[度]C)。更大的渗透梯度不会进一步增加MEPP频率。沐浴介质离子强度的变化不影响渗透效应对频率的影响。渗透压梯度对自发和神经冲动诱发的递质释放的影响之间的差异可以通过阻断神经末梢去极化的渗透效应来解释。时间-过程研究表明，在含有20 mM-KCl的溶液中，MEPP频率随着渗透压的增加而增加，随后频率降低到低于对照水平，而在含有30 mM-KCl的溶液中，渗透压的变化对MEPP频率没有直接影响。渗透梯度增加可通过一种不依赖于钙离子和神经末梢去极化的机制释放递质。渗透梯度变化对递质释放的最初瞬时效应与神经末梢膜水流量有关，而后期效应与神经末梢体积变化有关。
When the frequency of miniature end-plate potentials (mepps) was measured at neuromuscular junctions in rat diaphragm nerve preparations in vitro bathed in solutions having osmolarities between 200 and 700 m-os-moles/1., mepp frequency was transiently increased by exposure to osmotic gradients exceeding 75 m-osmoles/1., and then declined, within 1 hr. to a steady level slightly higher than the control level of frequency. Smaller osmotic gradients caused a maintained increase in mepp frequency. Epp quantal content was initially increased and later profoundly decreased upon exposure of preparations to solutions with an osmotic pressure of 500 or 600 m-osmoles/l. but was unaffected by less hypertonic solutions. Variation of the Ca or Mg content of the bathing solutions did not alter these effects of osmotic pressure on the early transient increase in mepp frequency or epp quantal content but affected the late steady increase in mepp frequency. The value of the transient increase in mepp frequency was exponentially related to the osmotic gradient in the range 0-300 m-osmoles/1. with a Qio of 1.95 (range il-34[degree]C). Greater osmotic gradients did not further increase mepp frequency. Variation of the ionic strength of the bathing medium did not influence osmotic effects upon frequency. The discrepancy between the effects of osmotic gradients upon spontaneous and nerve-impulse induced transmitter release was explained by an occlusion of the osmotic effects by depolarization of nerve terminals. Time-course studies showed that in the presence of 20 mM-KCl the mepp frequency increase in response to an increase in osmotic pressure was small and was followed by a reduction in frequency to below control levels while osmotic pressure changes had no immediate effect upon mepp frequency in solutions containing 30 mM-KCl. Increased osmotic gradients could release transmitter by a mechanism independent of Ca and of nerve terminal depolarization. The initial transient effects of changes of osmotic gradient upon transmitter release are related to flow of water through the nerve terminal membrane, while the later effects are related to nerve terminal volume changes.