An apparatus for controlling insertion of a membrane channel into a membrane, comprising: a first electrode configured to contact a first liquid in contact with a first surface of the membrane; a second electrode configured to contact a second liquid in contact with a second surface of the membrane, wherein the membrane separates the first and second liquids; and a driving unit configured to apply a potential difference across the membrane via the first and second electrodes (14, 16) to promote insertion of a membrane channel into the membrane from the first liquid or the second liquid, characterized in that: the apparatus comprises a membrane voltage reduction unit connected in series with the membrane; the driving unit is configured to apply a driving voltage across the membrane voltage reduction unit and the membrane, the driving voltage providing the potential difference across the membrane; and the membrane voltage reduction unit is configured such that a reduction in resistance through the membrane caused by insertion of a membrane channel intrinsically increases a potential difference across the membrane voltage reduction unit thereby lowering the potential difference across the membrane, wherein the lowering of the potential difference across the membrane is sufficient to prevent or reduce promotion of insertion of a further membrane channel. a first electrode configured to contact a first liquid in contact with a first surface of the membrane; a second electrode configured to contact a second liquid in contact with a second surface of the membrane, wherein the membrane separates the first and second liquids; and a driving unit configured to apply a potential difference across the membrane via the first and second electrodes (14, 16) to promote insertion of a membrane channel into the membrane from the first liquid or the second liquid, characterized in that: the apparatus comprises a membrane voltage reduction unit connected in series with the membrane; the driving unit is configured to apply a driving voltage across the membrane voltage reduction unit and the membrane, the driving voltage providing the potential difference across the membrane; and the membrane voltage reduction unit is configured such that a reduction in resistance through the membrane caused by insertion of a membrane channel intrinsically increases a potential difference across the membrane voltage reduction unit thereby lowering the potential difference across the membrane, wherein the lowering of the potential difference across the membrane is sufficient to prevent or reduce promotion of insertion of a further membrane channel. the apparatus comprises a membrane voltage reduction unit connected in series with the membrane; the driving unit is configured to apply a driving voltage across the membrane voltage reduction unit and the membrane, the driving voltage providing the potential difference across the membrane; and the membrane voltage reduction unit is configured such that a reduction in resistance through the membrane caused by insertion of a membrane channel intrinsically increases a potential difference across the membrane voltage reduction unit thereby lowering the potential difference across the membrane, wherein the lowering of the potential difference across the membrane is sufficient to prevent or reduce promotion of insertion of a further membrane channel.