To address whether the secreted PTH increases [Ca2+]i in keratinocytes, we first monitored [Ca2+]i following the addition of hPTH1-34 agonist (1 nM and 1 μM) in the culture medium of C5N (derived from normal mouse keratinocytes) and B9 (derived from mouse squamous cell carcinoma) cells. Here, PTH is linked to squamous cell carcinoma.