The extracellular solution used in ratio-metric [Ca2+]i measurements contained (in mM) 137 NaCl, 5 KCl, 1.8 CaCl2, 1 MgCl2, 10 Glucose and 10 Hepes, pH 7.4. Cells were incubated with 2 μM Fura-2 acetoxymethyl ester (Tef Labs Austin, TX) for 30 min. at room temperature.