Contractility and Ca2+ Signaling of Smooth Muscle Cells in Different Generations of Mouse Airways

The control and mechanisms of airway smooth muscle cell (SMC) contraction were investigated with a sequential series of lung slices from different generations of the same airway from the cardiac lobe of the mouse lung. Airway contraction was measured by monitoring the changes in airway lumen area with phase-contrast microscopy. Changes in intracellular calcium concentration of the SMCs were studied with a custom-built confocal or two-photon microscope. The distribution of the airway SMCs and the muscarinic M3 or 5-HT2A receptors was determined with immunofluorescence. Methacholine and 5-HT induced a concentration-dependent airway contraction and Ca2+ oscillations within the SMCs of each airway generation. The airway contraction in response to the same agonist concentration was greater in the middle generation compared with the distal or proximal generations of the same airway. Similarly, the Ca2+ oscillations varied in different generations of the same airway, with a slower frequency in the SMCs of the di...