Role of neuropeptide-sensitive L-type Ca2+ channels in histamine release in gastric enterochromaffin-like cells

Abstract

Peptides release histamine from enterochromaffin-like (ECL) cells because of elevation of intracellular Ca2+concentration ([Ca2+]i) by either receptor-operated or voltage-dependent Ca2+ channels (VDCC). To determine whether VDCCs contribute to histamine release stimulated by gastrin or pituitary adenylate cyclase-activating polypeptide (PACAP), the presence of VDCCs and their possible modulation by peptides was investigated in a 48-h cultured rat gastric cell population containing 85% ECL cells. Video imaging of fura 2-loaded cells was used to measure [Ca2+]i, and histamine was assayed by RIA. Cells were depolarized by increasing extracellular K+ concentrations or by 20 mM tetraethylammonium (TEA+). Cell depolarization increased transient and steady-state [Ca2+]iand resulted in histamine release, dependent on extracellular Ca2+. These K+- or TEA+-dependent effects on histamine release from ECL cells were coupled to activation of parietal cells in intact rabbit gastric glands, and L-type channel blockade by 2 μM nifedipine inhibited 50% of [Ca2+]i elevation and histamine release. N-type channel blockade by 1 μM ω-conotoxin GVIA inhibited 25% of [Ca2+]i elevation and 14% of histamine release. Inhibition was additive. The effects of 20 mM TEA+ were fully inhibited by 2 μM nifedipine. Both classes of Ca2+ channels were found in ECL cells, but not in parietal cells, by RT-PCR. Nifedipine reduced PACAP-induced (but not gastrin-stimulated) Ca2+ entry and histamine release by 40%. Somatostatin, peptide YY (PYY), and galanin dose dependently inhibited L-type Ca2+ channels via a pertussis toxin-sensitive pathway. L-type VDCCs play a role in PACAP but not gastrin stimulation of histamine release from ECL cells, and the channel opening is inhibited by somatostatin, PYY, and galanin by interaction with a Gi or Go protein.