EFFECTS OF CHANGES IN TEMPERATURE AND IONIC ENVIRONMENT ON THE POST-TETANIC POTENTIATION IN THE PHRENIC NERVE-DIAPHRAGM PREPARATION OF THE RAT

[摘要] References(38)Cited-By(4)It seems to be a general phenomenon in the neuromuscular junction that the response to single shocks following the tetanic stimulation of the motor nerve is regularly potentiated than the pre-tetanic one for a limited time. This phenomenon, the post-tetanic potentiation (PTP), has been shown to occur at a large number of synapses (1): the neuromuscular junction, the spinal cord, the autonomic ganglia, the hippocampus, the amygdala, the globus pallidus, and the sensory systems. The hypotheses explaining a mechanism of PTP in the neuromuscular junction have been introduced by many investigators. These are classified as follows: (a) PTP is attributed to a post-tetanic increase in transmitter release per nerve stimulation from the motor nerve terminals (2-4). (b) PTP is due to a temporal summation of the post-tetanic repetitive activity which is generated in the motor nerve terminals and is transmitted to the muscles (5-7). (c) Swelling of the pre-synaptic terminals following an application of tetanus causes a facilitated synaptic transmission, which is a cause of PTP (8). (d) PTP is explained in terms of a post-tetanic increase in the external potassium ion concentration because an increase in the potassium ion produces effects similar to those produced by tetanus (9-11). (e) PTP is accounted for by the change occurred in the muscle contractile mechanism or the increased contractile strenght of the muscle fibers (12, 13). Although no direct evidences have been obtained to explain the mechanism of PTP, many investigators have favoured the hypothesis that PTP is accounted for by the acceleration of the transmission mechanism in the pre-synaptic terminals. The prupose of the present experiments is to investigate effects of changes in temperature and ionic environment on PTP in the isolated rat phrenic nerve-diaphragm preparation, which may throw some light upon an elucidation of the mechanism of PTP. A preliminary report has been published in This Journal (14).

[学科分类] 药理学