Spontaneous release of transmitter from the growth cones of XXXX neurons in vitro: the influence of Ca2+ and Mg2+ ions.

@entity1238 @entity8723 @entity460 @entity3282 @entity1760
To determine whether spontaneous release of transmitter from the growth cones of neurons exhibits properties similar to the spontaneous release which occurs from the neurons at the neuromuscular junction, release of transmitter from the growth cones of @entity1238 neurons in culture was monitored in salines containing varying @entity460 and @entity1760 concentrations. Release was monitored by use of an outside-out piece of muscle membrane attached to a patch clamp electrode. Spontaneous release of transmitter from the growth cones in standard saline (2 mM @entity3282 , 1 mM @entity8723 ) produces clusters of single-channel openings in the muscle membrane. Clusters are seen to consist of two types: a series of high-frequency channel openings, called "bursts," and clusters of low-frequency channel openings called "singles." The bursts were identified and examined for their possible relationship to MEPP-producing release, and the singles were identified and examined for their possible relationship to "leak" release of the neuromuscular junction. When the external saline contains high @entity460 (10 mM @entity3282 , 1 mM @entity8723 ) or high @entity1760 (2 mM @entity3282 , 9 mM @entity8723 ), the frequencies of both "bursts" and "singles" was greatly reduced. This reduction in release persists if the neurons are grown in the high- @entity460 or high- @entity1760 solutions. When the saline is a low- @entity460 solution (0 mM @entity3282 , 3 mM @entity8723 ) the growth cones release transmitter at rates similar to those from standard saline. These results indicate that although the spontaneous release from the growth cone shares one characteristic with the leak release, neither the burst nor the singles release from the growth cones share exact relationship with either the MEPP producing release or the leak release. This suggests that further development of the mechanisms for spontaneous release of neurotransmitter occurs after nerve-muscle contact.
