Calcium receptor message, expression and function decrease in differentiating keratinocytes

Calcium-sensing receptor (CaSR) expression and function were studied in proliferating and differentiating cultured human gingival keratinocytes (HGKs). CaSR mRNA and protein were present in proliferating HGKs cultured in 0.03 mM [Ca2+] and decreased in cells induced to differentiate by culturing in 1.2 mM [Ca2+] for 2 days. CaSR protein was also detected in gingival tissue. Exposure to 10 mM extracellular [Ca2+] activated two sequential whole-cell currents. The first was a small, transient calcium release activated calcium current I-CRAC-like current with an inwardly rectifying I-V curve. The second current was larger with a linear I-V curve. Both currents were significantly decreased in differentiating cells. Neither neomycin nor gadolinium induced changes in whole cell currents nor in intracellular [Ca2+], but neomycin inhibited the late large current. Extracellular Ca2+ increased intracellular [Ca2+] of proliferating HGKs in a dose-dependent fashion. Comparison of the time-courses of the whole-cell currents and the intracellular [Ca2+] responses indicated both induced currents supported a Ca2+ influx. Extracellular [Mg2+] changes did not affect intracellular [Ca2+]. La3+ and 2-APB inhibited the whole cell current and intracellular [Ca2+] changes. The results indicate that the CaSR signaling response likely plays a major role in initiating Ca2+ induced differentiation responses in HGKs.