Question: where are ligand-gated ion channels found in cells
[{'answer': 'cell membrane', 'provenance': [{'wikipedia_id': '1351369', 'title': 'Ligand-gated ion channel', 'start_paragraph_id': 2, 'start_character': 338, 'end_paragraph_id': 2, 'end_character': 351, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '1351369', 'title': 'Ligand-gated ion channel', 'start_paragraph_id': 2, 'start_character': 0, 'end_paragraph_id': 2, 'end_character': 491, 'bleu_score': 0.9731482306711111, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 1368655229565022683}, 'section': 'Section::::Abstract.'}]}]