PLASMA-MEMBRANE CALCIUM-ATPASE IN SYNAPTIC TERMINALS OF CHICK EDINGER-WESTPHAL NEURONS

The plasma membrane calcium ATPase pump (PMCA) is one of two major mec hanisms known to be involved in extruding calcium from cells. The mono clonal antibody 5F10 was used to examine the distribution of PMCA in c hick Edinger-Westphal neurons, a population of cholinergic preganglion ic neurons whose cells bodies reside in the Edinger-Westphal nucleus i n the brainstem and whose axons form synaptic terminals on parasympath etic neurons in the ciliary ganglion. Definitive PMCA immunoreactivity was undetectable in Edinger-Westphal cell bodies in the brainstem. In contrast, immunoreactivity for PMCA was robust in ciliary ganglia and resembled patterns of immunoreactivity for the synaptic vesicle antig en SV-2, suggesting that PMCA is expressed in Edinger-Westphal synapti c terminals. Moreover, PMCA immunoreactivity co-localized with immunor eactivity for enkephalin and substance P, two neuropeptides known to b e expressed in Edinger-Westphal synaptic terminals. Fine structure stu dies revealed that PMCA immunoreactivity is associated with synaptic v esicles rather than the plasma membrane in Edinger-Westphal terminals. In immunodot assays, synaptic vesicles purified from Torpedo electric organ are also immunoreactive for PMCA as well as SV-2. Torpedo vesic les are negative for the sarcoplasmic/endoplasmic reticulum ATPase, su ggesting that the observed PMCA immunoreactivity is not associated wit h smooth endoplasmic reticulum. Immunoblot analysis confirmed that 5F1 0 recognizes a protein with the correct molecular mass for PMCA in tis sue homogenates of chick cerebellum, chick ciliary ganglia, and Torped o synaptic vesicles. These findings describe a previously unrecogized location for PMCA in the membranes of cholinergic synaptic vesicles. R elevance to previous data and possible functions are discussed.