L-type calcium channels in enterochromaffin cells from guinea pig and human duodenal crypts:: An in situ study

Background & Aims: This study has investigated stimulus-secretion coupling of enterochromaffin cells by studying the cellular location and function of voltage-gated Ca2+ channels within small intestinal crypts, Methods: Digital fluorescence imaging and electrochemical detection were used to measure intracellular Ca2+ responses and serotonin (5-hydroxytryptamine [5-HT]) secretion in intact crypts isolated from guinea pig and human duodenum. Results: In fluo-3-loaded crypts, electrical depolarization with high K+ solution increased cytosolic free [Ca2+] only in single cells subsequently identified by immunocytochemistry as enterochromaffin cells. In guinea pig enterochromaffin cells, the L-type Ca2+ channel agonist FPL 64176 (3 mu mol/L) did not change resting intracellular [Ca2+] but potentiated the depolarization-evoked increase in [Ca2+] (298 +/- 72 nmol/L) by 19 +/- 3-fold. In the majority of human enterochromaffin cells, FPL 64176 alone increased resting [Ca2+] by 423 +/- 171 nmol/L. Secretion studies in guinea pig crypts showed that high K+ and FPL 64176 caused a 12-fold increase in 5-HT release, Noradrenaline caused increases in both enterochromaffin cell [Ca2+] and 5-HT release, Conclusions: Using this approach, we have found that in duodenal crypts, enterochromaffin cells, but not other epithelial cells, contain L-type voltage-gated Ca2+ channels involved in regulating 5-HT secretion, These data have implications for the pharmacological control of intestinal disorders involving enterochromaffin cell dysfunction.