Method for efficiently producing β myosin heavy chain in cardiac muscle cells differentiated from induced pluripotent stem cells derived from

1. A method for producing a β myosin heavy chain in cardiac muscle cells differentiated from human induced pluripotent stem cells, the method comprising:

(a) supplying a liquid culture medium containing the cardiac muscle cells onto a substrate comprising a first electrode, a second electrode and insulative fibers on the surface thereof to coat a surface of the first electrode, a surface of the second electrode, and a region between the first electrode and the second electrode with the cardiac muscle cells;

wherein

at least a part of the insulative fibers is located between the first electrode and the second electrode in a top view of the substrate; and

an angle formed between each of not less than 90% of the insulative fibers and an imaginary straight line which passes through both the first electrode and the second electrode is not more than ±20 degrees in the top view;

(b) leaving the substrate at rest;

(c) cultivating the cardiac muscle cells, while a pulse electric current is applied to the cardiac muscle cells through the first electrode and the second electrode; and

(d) obtaining the β myosin heavy chain produced in the cultivated cardiac muscle cells.

2. The method according to claim 1 , wherein in the step (b), the substrate is left at rest until the cardiac muscle cells adhere on the surface of the substrate or the insulative fibers.

3. The method according to claim 1 , wherein a reference electrode is in contact with the liquid culture medium.

4. The method according to claim 3 , wherein the reference electrode is grounded.

5. The method according to claim 3 , wherein the substrate comprises the reference electrode on the surface thereof.

6. The method according to claim 3 , wherein the liquid culture medium includes the reference electrode.