Activation of histamine H3 receptor decreased cytoplasmic Ca(2+) imaging during electrical stimulation in the skeletal myotubes.

Histamine is a neurotransmitter and chemical mediator in multiple physiological processes. Histamine H3 receptor is expressed in the nervous system, heart, and gastrointestinal tract; however, little is known about H3 receptor in skeletal muscle. The aim of this study was to investigate the role of H3 receptor in skeletal myotubes. The expression of H3 receptor and myosin heavy chain (MHC), a late myogenesis marker, was assessed by real-time PCR and immunostaining in C2C12 skeletal myogenesis and adult mid-urethral skeletal muscle tissues. H3 receptor mRNA showed a significant increase upon differentiation of C2C12 into myotubes: 1-, 26-, 91-, and 182-fold at days 0, 2, 4, and 6, respectively. H3 receptor immunostaining in differentiated C2C12 cells and adult skeletal muscles was positive and correlated with that of MHC. The functional role of H3receptor in differentiated myotubes was assessed using an H3 receptor agonist, (R)-a-methylhistamine ((R)-α-MeHA). Ca(2+) imaging, stimulated by electric pacing, was decreased by 55% after the treatment of mature C2C12 myotubes with 1μM (R)-α-MeHA for 10min and 20min, while treatment with 100nm (R)-α-MeHA for 5min caused 45% inhibition. These results suggested that H3 receptor may participate in the maintenance of the relaxed state and prevention of over-contraction in mature differentiated myotubes. The elucidation of the role of H3R in skeletal myogenesis and adult skeletal muscle may open a new direction in the treatment of skeletal muscle disorders, such as muscle weakness, atrophy, and myotonia in motion systems or peri-urethral skeletal muscle tissues.