Spatial and temporal aspects of ACh-induced [Ca2+]i oscillations in porcine tracheal smooth muscle

This study evaluated the relationship between regional elevation in intracellular calcium concentration ([Ca2+]i) induced by acetylcholine (ACh) and the global cellular responses in porcine tracheal smooth muscle (TSM) cells. Regional (approximately 1.5 microm3) and global (whole cell) changes in [Ca2+]i were measured in fluo-3 loaded TSM cells using real-time confocal microscopy. Regional responses appeared as propagating [Ca2+]i oscillations whereas global responses reflected the spatiotemporal integration of these regional responses. Within a region, [Ca2+]i oscillations were 'biphasic' with initial higher frequencies, followed by slower steady-state oscillations. With increasing ACh concentration, the peak (maximum value relative to 0 nM) of regional [Ca2+]i oscillations remained relatively constant, whereas both frequency and propagation velocity increased. In contrast, the global spatiotemporal integration of the regional oscillatory responses appeared as a concentration-dependent increase in peak as well as mean cellular [Ca2+]i. We conclude that the significance of ACh-induced [Ca2+]i oscillations lies in the establishment of mean [Ca2+]i level for slower Ca2+-dependent physiological processes via modulation of oscillation frequency and propagation velocity.