Intracellular Ca2+ can be conveniently monitored by sensitive Ca2+ fluorescent dyes in live cells. The Gαq involved lipid signaling pathways and, thus, can be studied by intracellular Ca2+ imaging. Here we describe the protocols to measure intracellular Ca2+ for studying PEG2-EP1 activity in esophageal smooth muscle cells. The ratiometric Fura-2 imaging provides quantitative data, and the Fluo-4 confocal microscopic imaging has high-spatial resolution.

Store-operated Ca2+ entry (SOCE) pathway plays important roles in many cellular processes, which is largely studied by using fluorescent Ca2+ indicator, Fura-2. Extracellular Mn2+ is able to cross the plasma membrane through SOCE and quenches the fluorescence signals from Fura-2. Thus, the fluorescence quenching rate by Mn2+ composes a convenient assay to monitor the extent of SOCE. This chapter describes an experimental method of Mn2+ quenching assay for both cultured esophageal epithelial and skeletal muscle cells. It also explains how to perform a quantitative analysis of graded SOCE.