def ab_pull(monolayer, cell, radial_tension, distributed=False):
    """Adds a linear tension to the apical-to-basal edges
    of a cell
    """
    cell_edges = monolayer.edge_df[monolayer.edge_df['cell'] == cell]
    lateral_edges = cell_edges[cell_edges['segment'] == 'lateral']
    srce_segment = monolayer.upcast_srce(monolayer.vert_df['segment']).loc[
        lateral_edges.index]
    trgt_segment = monolayer.upcast_trgt(monolayer.vert_df['segment']).loc[
        lateral_edges.index]
    ab_edges = lateral_edges[(srce_segment == 'apical') & (trgt_segment ==
        'basal')].index
    ba_edges = lateral_edges[(trgt_segment == 'apical') & (srce_segment ==
        'basal')].index
    if distributed:
        new_tension = radial_tension / (len(ab_edges) + len(ba_edges))
    else:
        new_tension = radial_tension
    monolayer.edge_df.loc[ab_edges, 'line_tension'] += new_tension
    monolayer.edge_df.loc[ba_edges, 'line_tension'] += new_tension
