Activation of histamine H3 receptor decreased cytoplasmic Ca2+ imaging during electrical stimulation in the skeletal myotubes

Abstract Histamine is a neurotransmitter and chemical mediator in multiple physiological processes. Histamine H 3 receptor is expressed in the nervous system, heart, and gastrointestinal tract; however, little is known about H 3 receptor in skeletal muscle. The aim of this study was to investigate the role of H 3 receptor in skeletal myotubes. The expression of H 3 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. H 3 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. H 3 receptor immunostaining in differentiated C2C12 cells and adult skeletal muscles was positive and correlated with that of MHC. The functional role of H 3 receptor in differentiated myotubes was assessed using an H 3 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 1 μM (R)-α-MeHA for 10 min and 20 min, while treatment with 100 nm (R)-α-MeHA for 5 min caused 45% inhibition. These results suggested that H 3 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 H 3 R 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.