Effects of TNFα on Dynamic Cytosolic Ca(2 +) and Force Responses to Muscarinic Stimulation in Airway Smooth Muscle

Previously, we reported that in airway smooth muscle (ASM), the cytosolic Ca(2+) ([Ca(2+)](cyt)) and force response induced by acetyl choline (ACh) are increased by exposure to the pro-inflammatory cytokine tumor necrosis factor α (TNFα). The increase in ASM force induced by TNFα was not associated with an increase in regulatory myosin light chain (rMLC(20)) phosphorylation but was associated with an increase in contractile protein (actin and myosin) concentration and an enhancement of Ca(2+) dependent actin polymerization. The sensitivity of ASM force generation to elevated [Ca(2+)](cyt) (Ca(2+) sensitivity) is dynamic involving both the shorter-term canonical calmodulin-myosin light chain kinase (MLCK) signaling cascade that regulates rMLC(20) phosphorylation and cross-bridge recruitment as well as the longer-term regulation of actin polymerization that regulates contractile unit recruitment and actin tethering to the cortical cytoskeleton. In this study, we simultaneously measured [Ca(2+)](cyt) and force responses to ACh and explored the impact of 24-h TNFα on the dynamic relationship between [Ca(2+)](cyt) and force responses. The temporal delay between the onset of [Ca(2+)](cyt) and force responses was not affected by TNFα. Similarly, the rates of rise of [Ca(2+)](cyt) and force responses were not affected by TNFα. The absence of an impact of TNFα on the short delay relationships between [Ca(2+)](cyt) and force was consistent with the absence of an effect of [Ca(2+)](cyt) and force on rMLC(20) phosphorylation. However, the integral of the phase-loop plot of [Ca(2+)](cyt) and force increased with TNFα, consistent with an impact on actin polymerization and, contractile unit recruitment and actin tethering to the cortical cytoskeleton.