GEOMETRY, KINETICS AND PLASTICITY OF RELEASE AND CLEARANCE OF ATP ANDNORADRENALINE AS SYMPATHETIC COTRANSMITTERS - ROLES FOR THE NEUROGENIC CONTRACTION

Citation
L. Stjarne et E. Stjarne, GEOMETRY, KINETICS AND PLASTICITY OF RELEASE AND CLEARANCE OF ATP ANDNORADRENALINE AS SYMPATHETIC COTRANSMITTERS - ROLES FOR THE NEUROGENIC CONTRACTION, Progress in neurobiology, 47(1), 1995, pp. 45-94
Citations number
168
Categorie Soggetti
Neurosciences
Journal title
ISSN journal
03010082
Volume
47
Issue
1
Year of publication
1995
Pages
45 - 94
Database
ISI
SICI code
0301-0082(1995)47:1<45:GKAPOR>2.0.ZU;2-N
Abstract
The paper compares the microphysiology of sympathetic neuromuscular tr ansmission in three model preparations: the guinea-pig and mouse vas d eferens and rat tail artery. The first section describes the quantal r elease of ATP and noradrenaline from individual sites. The data are pr oposed to support a string model in which: (i) most sites (greater tha n or equal to 99%) ignore the nerve impulse and a few (less than or eq ual to 1%) release a single quantum of ATP and noradrenaline; (ii) the probability of monoquantal release is extremely non-uniform; (iii) hi gh probability varicosities form 'active' strings; and (iv) an impulse train causes repeated quantal release from these sites. Analogy with molecular mechanisms regulating transmitter exocytosis in other system s is proposed to imply that coincidence of at least two factors at the active zone, Ca2+ and specific cytosolic protein(s), may be required to remove a 'fusion clamp', form a 'fusion complex' and trigger exocyt osis of a sympathetic transmitter quantum, and that the availability o f these proteins may regulate the release probability. The second sect ion shows that clearance of noradrenaline in rat tail artery is basica lly greater than or equal to 30-fold slower than of co-reIeased ATP, a nd that saturation of local reuptake and binding to local buffering si tes maintain the noradrenaline concentration at the receptors, in spit e of a profound decline in per pulse release during high frequency tra ins. The third section describes differences in the strategies by whic h mouse vas deferens and rat tail artery use ATP and noradrenaline to trigger and maintain the neurogenic contraction.