Schematic diagram of the methods used to apply mechanical force (a) and electrical load (b). For application of mechanical force, the hook moves up and down twice per minute in the direction of the arrow (a). For electrical stimulation, the electrical circuit consists of a pair of electrode baths containing DMEM with 10% FBS and 1% P/S, a pair of agar bridges (8 cm long) made of phosphate buffer saline (PBS) gelled by 2% agar, and a pair of electrode baths containing PBS; electrical current was supplied by a 9 V dry battery (b).