Characterization of the role of calcium and sodium channels in the stimulus secretion coupling of 5-hydroxytryptamine release from porcine enterochromaffin cells

Abstract

Strips of the porcine small intestine were incubated in vitro and the outflow of 5-hydroxytryptamine (5-HT) was determined by HPLC with electrochemical detection. Spontaneous outflow of 5-HT from the porcine small intestine was reduced by about 70% after removal of the extracellular calcium or by addition of 1 mM gadolinium. Tetrodotoxin reduced the outflow of 5-HT by 30%, an effect which has previously been shown to be caused by inhibition of an excitatory cholinergic input. The sodium channel opener veratridine (up to 100 microM) did not affect the outflow of 5-HT. omega-Conotoxin GVIA (500 nM) or nifedipine (10 microM) reduced the outflow of 5-HT only by about 50%, and their effects were not additive. The inhibitory effects of omega-conotoxin GVIA occurred also in the presence of tetrodotoxin. Elevation of extracellular potassium to 40 mM caused a marked and sustained increase in 5-HT outflow. High potassium evoked release of 5-HT was blocked by omega-conotoxin GVIA, nifedipine and gadolinium. When omega-conotoxin GVIA and nifedipine were present in combination, their inhibitory effects on the high potassium evoked 5-HT release vanished. BAY K 8644 (1-10 microM) did not facilitate 5-HT release, but markedly reduced the spontaneous and high potassium evoked release of 5-HT. In conclusion, the enterochromaffin cells are endowed with multiple calcium channels, but voltage-sensitive calcium channels of a neuronal L-type which are sensitive to dihydropyridines and omega-conotoxin GVIA appear to play a major role.

Differential Distribution of Serotonin and Tryptophan Hydroxylase in the Human Gastrointestinal Tract

“…In preparations of isolated enterochromaffin cells, the spontaneous activity of tryptophan hydroxylase was found to be relatively low, since a significant synthesis of [ 14 C]5-hydroxytryptamine from [ 14 C]tryptophan was only detected after prolonged (24 h) exposure to [ 14 C]tryptophan [19]. These functional studies also demonstrated that enterochromaffin cells contain a 5-hydroxytryptophan decarboxylating enzyme.…”

“…The aromatic L -amino acid decarboxylase then converts 5-hydroxytryptophan to 5-hydroxytryptamine, which is released either as plasma-free or platelet-bound serotonin into the systemic circulation. It is well established that enterochromaffin cells can release 5-hydroxytryptamine from specific secretory vesicles in a calcium-dependent manner [19, 20]. …”

Differential localization of Ca2+ channel ?1 subunits in the enteric nervous system: Presence of ?1B channel-like immunoreactivity in intrinsic primary afferent neurons

“…There is evidence that EC cells are endowed with voltage-regulated Ca 2ϩ channels, which have characteristics of L-type channels (Racké and Schwörer, 1993). Furthermore, 5-HT release evoked by depolarizing concentrations of potassium is blocked by the dihydropyridine, nifedipine (Racké et al, 1996); however, secretion of 5-HT evoked by stimulation of muscarinic receptors occurs in the presence of nifedipine (Racké and Schwörer, 1993). Thus, the modulation of 5-HT secretion by Ca 2ϩ channel blockers appears to be stimulus-specific.…”

“…EC cells are thought to sense changes in the lumen of the gut and to transmit this sensory signal to the mucosal processes of intrinsic primary afferent neurons by the release of 5-HT (Bü lbring and Lin, 1958;Bü lbring and Crema, 1959;Kirchgessner et al, 1992). There is evidence that EC cells are endowed with voltage-regulated Ca 2ϩ channels, which have characteristics of L-type channels (Racké and Schwörer, 1993). Furthermore, 5-HT release evoked by depolarizing concentrations of potassium is blocked by the dihydropyridine, nifedipine (Racké et al, 1996); however, secretion of 5-HT evoked by stimulation of muscarinic receptors occurs in the presence of nifedipine (Racké and Schwörer, 1993).…”

Neuroendocrine Cells along the Digestive Tract Express Neuropilin-2

“…The binding of semaphorin-3A to np-1 induces the opening of calcium channels in the cell membrane (33). Calcium influx is associated with the regulation of neurotransmitter release in nerve cells (34), and can induce the release of serotonin from small cell lung carcinoma cells (35), and from serotonin releasing cells in the gut (36). The np-2 agonist semaphorin-3F contains the same consensus sequence which had been shown to mediate the interaction of semaphorin 3A with calcium channels following its binding to np-1 (33).…”