Author:

Keywords:

Science & Technology, Life Sciences & Biomedicine, Biochemistry & Molecular Biology, Cell Biology, Respiratory System, airway smooth muscle, asthma, thermoplasty, myosin, TRPV channels, SMOOTH-MUSCLE, REVERSIBLE PHOSPHORYLATION, CAPSAICIN-RECEPTOR, CATION CHANNELS, HIGH-THRESHOLD, LIGHT-CHAIN, TRPV2, EXPRESSION, ACTIVATION, ASTHMA, Acetylcholine, Actins, Animals, Bronchi, Cattle, Hot Temperature, In Vitro Techniques, Isometric Contraction, Isoproterenol, Muscle, Smooth, Myosin-Light-Chain Kinase, Myosins, Protein Denaturation, TRPV Cation Channels, Trachea, 1102 Cardiorespiratory Medicine and Haematology, 3101 Biochemistry and cell biology, 3201 Cardiovascular medicine and haematology

Abstract:

Despite the emerging use of bronchial thermoplasty in asthma therapy, the response of airway smooth muscle (ASM) to extreme temperatures is unknown. We sought here to investigate the immediate effects (as opposed to changes occurring beyond a few days). Isometric contractions were studied in bovine ASM before and after exposure to various thermal loads and/or pharmacological interventions. Actin-myosin interactions were investigated using a standard in vitro motility assay. We found a steep thermal sensitivity for isometric contractions evoked by acetylcholine, with threshold and complete inhibition at <50 degrees C and >55 degrees C, respectively. Contractile responses to serotonin or KCl were similarly affected, while isometric relaxations evoked by the nitric oxide donor S-nitrosyl-N-acetylpenicillamine or the beta-agonist isoproterenol were unaffected. This thermal sensitivity developed within 15 minutes, but did not evolve further over the course of several days (rules out heat shock proteins, apoptosis, autophagy, necrosis, etc.). Although heat-sensitive TRPV2 channels and Cam kinase II-induced inactivation of myosin light chain kinase are both acutely thermally sensitive with T1/2 of 52.5 degrees C, the phenomenon which we describe was not prevented by blockers of TRPV2 channels (ruthenium red; gadolinium; zero-Ca2+ or zero-Na+/zero-Ca2+ media; cromakalim), nor of Cam kinase II (W7; trifluoperazine; KN-93). However, direct measurements of actin-myosin interactions showed the same steep thermal profile. We conclude that extreme temperatures (such as those employed in bronchial thermoplasty) directly disrupt actin-myosin interaction, likely through a denaturation of the motor protein, leading to an immediate loss of ASM cell function.