Fig. 2. The Ca²⁺ response is preserved in DD keratinocytes. Normal and DD keratinocytes were cultured on glass coverslips in medium containing 0.06 mM Ca²⁺ until they were 50% confluent, then loaded with the Ca²⁺-sensitive dye Fura-2 (see Materials and Methods). The cells initially were superfused with control solution containing: 138 mM NaCl, 2.7 mM KCl, 1.5 mM KH₂PO₄, 1.0 mM Na₂HPO₄, 0.06 mM CaCl₂; 10 mM glucose, pH 7.4, 286 mOsm, then switched to this solution with 1.0 mM Ca²⁺ added (arrow). Although the baseline Ca²⁺ concentrations were much lower in DD keratinocytes, both normal and DD keratinocytes responded with a sustained increase in intracellular Ca²⁺ after exposure to raised extracellular Ca²⁺ levels. The absolute increase in intracellular Ca²⁺ was similar between DD and control keratinocytes, whereas the fold increase was significantly higher in DD keratinocytes (see Table 2).