Properties of a potassium channel in cultured human gastric cells (HGT-1) possessing specific omeprazole binding sites.
The HGT-1 human gastric cell line is similar to acid secreting parietal cells in that it possesses H2 receptors, histamine sensitive adenyl cyclase, and Cl- channels, which are activated by histamine by a cyclic adenosine monophosphate (cAMP) dependent mechanism. To discover if HGT-1 cells have additional properties found in parietal cells, [3H]omeprazole and patch clamp recording techniques were used to evaluate specific omeprazole binding sites and K+ channels in the plasma membrane. HGT-1 cells exhibited [3H]omeprazole binding in the non-stimulated state, which increased 100% in the presence of 1 mM histamine. High conductance (about 155 pS) K+ channels were active spontaneously in 17% of cell attached or excised inside out patches in non-stimulated subconfluent HGT-1 cells. In inside out patches, channel activity increased fivefold during depolarisation, ion substitution experiments confirmed that the channels were highly selective for K+, and channel activity was almost abolished by removal of Ca2+ or addition of 5 mM Ba2+. In quiescent cell attached patches, 0.1 mM dibutyryl cAMP failed to activate K+ channels. In contrast, 6.7 microM A23187 (a Ca2+ ionophore) increased intracellular Ca2+ concentration from mean (SEM) 14 (3) nM to 248 (30) nM and activated K+ channels in 21% of patches. It is concluded that the plasma membrane of HGT-1 cells possesses (a) specific 3H-omeprazole binding sites, which may reflect the omeprazole sensitive H+,K(+)-ATPase present in gastric parietal cells; and (b) Ca(2+)-activated K+ channels, which may be located in the basolateral membrane of human gastric parietal cells and play a part in acid secretion triggered by Ca(2+)-mediated secretory agonists.
Sandle
G I
GI
Manchester Epithelial Membrane Research Centre, Hope Hospital.
Fraser
G
G
Fogg
K
K
Warhurst
G
G
D001464:Barium / Q000494:pharmacology; D001665:Binding Sites; D003994:Bucladesine / Q000494:pharmacology; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology; D002478:Cells, Cultured; D005753:Gastric Mucosa / Q000378:metabolism*; D006632:Histamine / Q000494:pharmacology; D006801:Humans; D008564:Membrane Potentials / Q000187:drug effects; D009853:Omeprazole / Q000378:metabolism; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism*
D015221:Potassium Channels; D001464:Barium; D000001:Calcimycin; D003994:Bucladesine; D006632:Histamine; D009853:Omeprazole; D002118:Calcium