Ca(2+)-independent and Ca(2+)-dependent stimulation of quantal neurosecretion in avian ciliary ganglion neurons.
1. Although it is generally agreed that Ca2+ couples depolarization to the release of neurotransmitters, hypertonic saline and ethanol (ETOH) evoke neurosecretion independent of extracellular Ca2+. One possible explanation is that these agents release Ca2+ from an intracellular store that then stimulates Ca(2+)-dependent neurosecretion. An alternative explanation is that these agents act independently of Ca2+. 2. This work extends previous observations on the action of ETOH and hypertonic solutions (HOSM) on neurons to include effects on [Ca2+]i. We have looked for Ca(2+)-independent or -dependent neurosecretion evoked by these agents in parasympathetic postganglionic neurons dissociated from chick ciliary ganglia and maintained in tissue culture. The change in concentration of free Ca2+ in the micromolar range inside neurons ([Ca2+]i) was measured with indo-1 with the use of a Meridian ACAS 470 laser scanning microspectrophotometer. 3. Elevated concentration of extracellular KCl increased [Ca2+]i and the frequency of quantal events. Also, a twofold increase in osmotic pressure (HOSM) produced a similar increase in quantal release and a significant rise in [Ca2+]i; however, the Ca2+ appeared to come from intracellular stores. 4. In contrast, ETOH stimulated quantal neurosecretion without a measurable change in [Ca2+]i. It appears the alcohol exerts its influence on some stage in the process of exocytosis that is distal to or independent of the site of Ca2+ action. 5. The effects of high [KCl]o and osmotic pressure were occlusive. This is explained in part by the observation that hypertonicity reduced Ca2+ current, but an action on Ca2+ stores is also likely.(ABSTRACT TRUNCATED AT 250 WORDS)
Brosius
D C
DC
Department of Physiology, University of Virginia Health Science Center, Charlottesville 22908.
Hackett
J T
JT
Tuttle
J B
JB
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D002645:Chickens; D004594:Electrophysiology / Q000379:methods; D000431:Ethanol / Q000494:pharmacology; D005726:Ganglia, Parasympathetic / Q000187:drug effects / Q000502:physiology*; D006982:Hypertonic Solutions; D007700:Kinetics; D009132:Muscles / Q000294:innervation; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D009997:Osmotic Pressure; D011189:Potassium Chloride / Q000494:pharmacology
D006982:Hypertonic Solutions; D000431:Ethanol; D011189:Potassium Chloride; D002118:Calcium