TRPV4 Activation during Guinea Pig Airway Smooth Muscle Contraction Promotes Ca 2+ and Na + Influx.

Airway smooth muscle (ASM) contraction is determined by the increase in intracellular Ca 2+ concentration ([Ca 2+ ] i ) caused by its release from the sarcoplasmic reticulum (SR) or by extracellular Ca 2+ influx. Major channels involved in Ca 2+ influx in ASM cells are L-type voltage-dependent Ca 2+ channels (L-VDCCs) and nonselective cation channels (NSCCs). Transient receptor potential vanilloid 4 (TRPV4) is an NSCC recently studied in ASM. Mechanical stimuli, such as contraction, can activate TRPV4. We investigated the possible activation of TRPV4 by histamine (His)- or carbachol (CCh)-induced contraction in guinea pig ASM. In single myocytes, the TRPV4 agonist (GSK101) evoked an increase in [Ca 2+ ] i , characterized by a slow onset and a plateau phase. The TRPV4 antagonist (GSK219) decreased channel activity by 94%, whereas the Ca 2+ -free medium abolished the Ca 2+ response induced by GSK101. Moreover, GSK101 caused Na + influx in tracheal myocytes. GSK219 reduced the Ca 2+ peak and the Ca 2+ plateau triggered by His or CCh. TRPV4 blockade shifted the concentration-response curve relating to His and CCh to the right in tracheal rings and reduced the maximal contraction. Finally, the activation of TRPV4 in single myocytes increased the Ca 2+ refilling of the SR. We conclude that contraction of ASM cells after stimulation with His or CCh promotes TRPV4 activation, the subsequent influx of Ca 2+ and Na + , and the opening of L-VDCCs. The entry of Ca 2+ into ASM cells via TRPV4 and L-VDCCs contributes to optimal smooth muscle contraction.