A novel single-photon counting technique applied to highly sensitive measurement of [[[Ca.sup.2+]].sub.i] transient in human aortic smooth muscle cells

This study demonstrates that aequorin, a luminescent natural dye, is useful for vascular cell intracellular [Ca.sup.2+] concentration ([[[Ca.sup.2+]].sub.i]) determination. A new single-photon counting technique was developed to resolve the effects of fluid flow shear stress on [[[Ca.sup.2+]].sub.i] in human aortic smooth muscle cells (HASMCs). Confluent HASMCs were grown on petri dishes loaded with aequorin. Then the dishes were placed in a luminometer chamber after the physiological level of shear stress was applied to the HASMC surfaces. The chamber was housed inside a highly sensitive photomultiplier tube. It detected ultraweak photon emission in response to the [[[Ca.sup.2+]].sub.i] transient. In the presence of 2.0 mM extracellular [Ca.sup.2+], a shear stress of 12 dyn/[cm.sup.2], applied for 60 s to the top surface of the HASMC monolayer, elicited a sharp increase in [[[Ca.sup.2+]].sub.i]. [DOI: 10.1115/1.2264396] Keywords: ultraweak photon-counting, smooth muscle cells, shear stress, intracellular [Ca.sup.2+], biophoton