Gastrin and the neuropeptide PACAP evoke secretion from rat stomach histamine-containing (ECL) cells by stimulating influx of Ca2+ through different Ca2+ channels.
1. Gastrin and PACAP stimulate secretion of histamine and pancreastatin from isolated rat stomach ECL cells. We have examined whether or not secretion depends on the free cytosolic Ca2+ concentration ([Ca2+]i) and the pathways by which gastrin and PACAP elevate [Ca2+]i. Secretion was monitored by radioimmunoassay of pancreastatin and changes in [Ca2+]i by video imaging. The patch clamp technique was used to record whole-cell currents and membrane capacitance (reflecting exocytosis). 2. In the presence of 2 mM extracellular Ca2+, gastrin and PACAP induced secretion and raised [Ca2+]i. Without extracellular Ca2+ (or in the presence of La3+) no secretion occurred. The extracellular Ca2+ concentration required to stimulate secretion was 10 times higher for gastrin than for PACAP. Depletion of intracellular Ca2+ pools by thapsigargin had no effect on the capacity of gastrin and PACAP to stimulate secretion. 3. Gastrin-evoked secretion was inhibited 60-80 % by L-type channel blockers and 40 % by the N-type channel blocker omega-conotoxin GVIA. Combining L-type and N-type channel blockers did not result in greater inhibition than L-type channel blockers alone. Whole-cell patch clamp measurements confirmed that the ECL cells are equipped with voltage-dependent inward Ca2+ currents. A 500 ms depolarising pulse from -60 mV to +10 mV which maximally opened these channels resulted in an increase in membrane capacitance of 100 fF reflecting exocytosis of secretory vesicles. 4. PACAP-evoked secretion was reduced 40 % by L-type channel blockers but was not influenced by inhibition of N-type channels. SKF 96365, a blocker of both L-type and receptor-operated Ca2+ channels, inhibited PACAP-evoked secretion by 85 %. Combining L-type channel blockade with SKF 96365 abolished PACAP-evoked secretion. 5. The results indicate that gastrin- and PACAP-evoked secretion depends on Ca2+ entry and not on mobilisation of intracellular Ca2+. While gastrin stimulates secretion via voltage-dependent L-type and N-type Ca2+ channels, PACAP acts via L-type and receptor-operated Ca2+ channels.
Lindström
E
E
Institute of Physiological Sciences, Department of Pharmacology, University of Lund, Lund, Sweden. erik.lindstrom@farm.lu.se
Eliasson
L
L
Björkqvist
M
M
Håkanson
R
R
D000818:Animals; D002118:Calcium / Q000378:metabolism / Q000502:physiology*; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism*; D020013:Calcium Signaling / Q000187:drug effects*; D002478:Cells, Cultured; D002614:Chelating Agents / Q000494:pharmacology; D053379:Chromogranin A; D004533:Egtazic Acid / Q000494:pharmacology; D004594:Electrophysiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005089:Exocytosis / Q000187:drug effects; D005753:Gastric Mucosa / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D005755:Gastrins / Q000494:pharmacology*; D006636:Histamine Release / Q000187:drug effects*; D008297:Male; D018715:Microscopy, Video; D009479:Neuropeptides / Q000494:pharmacology*; D010187:Pancreatic Hormones / Q000378:metabolism; D051219:Pituitary Adenylate Cyclase-Activating Polypeptide; D051381:Rats; D017207:Rats, Sprague-Dawley; D015222:Sodium Channels / Q000187:drug effects; D019284:Thapsigargin / Q000494:pharmacology
C495403:Adcyap1 protein, rat; D015220:Calcium Channels; D002614:Chelating Agents; D053379:Chromogranin A; D004791:Enzyme Inhibitors; D005755:Gastrins; D009479:Neuropeptides; D010187:Pancreatic Hormones; D051219:Pituitary Adenylate Cyclase-Activating Polypeptide; D015222:Sodium Channels; C050836:pancreastatin; D004533:Egtazic Acid; D019284:Thapsigargin; D002118:Calcium