Kurjak M, Schusdziarra V, Allescher HD. Release of somatostatin-like immunoreactivity from enriched enteric nerve varicosities of rat ileum.
Eur J Pharmacol 1995;
281:295-301. [PMID:
8521913 DOI:
10.1016/0014-2999(95)00261-i]
[Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Synaptosomes were isolated from rat ileum by various steps of differential centrifugation. The peptide content for somatostatin-like immunoreactivity was used as marker for neuronal membranes. The enriched synaptosomal fraction (P2) showed a good enrichment of somatostatin content (4-fold) in comparison to the post-nuclear supernatant. The basal release of somatostatin-like immunoreactivity was 26 +/- 3 pg/mg tissue protein. KCl-evoked depolarization (65 mM) caused a significant increase of somatostatin-like immunoreactivity release (72 +/- 11 pg/mg, n = 12, P < 0.001) compared to basal release. In Ca(2+)-free medium the evoked release of somatostatin-like immunoreactivity was abolished. A substantial increase of somatostatin-like immunoreactivity release (52 +/- 7 pg/mg, n = 12, P < 0.05) was also observed in the presence of the Ca2+ ionophore A-23187. The cholinergic agonist carbachol elicited a dose-dependent release of somatostatin-like immunoreactivity (10(-7) M: 54 +/- 8 pg/mg, 10(-6) M: 63 +/- 6 pg/mg, 10(-5) M: 53 +/- 5 pg/mg, n = 12, P < 0.001), which was blocked by atropine (10(-6) M: 35 +/- 6 pg/mg, n = 12, P < 0.001), but not by hexamethonium. Other presynaptic modulating substances such as serotonin, the selective neurokinin-B agonist [beta Asp4,MePhe7]neurokinin B-(4-10), neurotensin, cholecystokinin-8, caerulein and pentagastrin had no stimulatory effect on release of somatostatin-like immunoreactivity. In summary, somatostatin-like immunoreactivity can be released from enteric synaptosomes by both depolarization with KCl and cholinergic stimulation via a muscarinic mechanism. The synaptosomes of intrinsic nerves offer an approach to study release of neuronal somatostatin on the subcellular level.
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