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 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 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. <EOS>