Regulation of cytosolic calcium by parathyroid hormone and oscillations of cytosolic calcium in fibroblasts from normal and pseudohypopara- thyroid patients

The second messengers for PTH action on fi-broblasts have not been determined. The hypothesis that Ca²⁺is a second messenger was examined by spectrofluorometric measurement of cytosolic calcium ([Ca²⁺]_i) of fura-2-loaded hu-man dermal skin fibroblasts. PTH induced: 1) transient eleva-tions of [Ca²⁺]_idue to both Ca²⁺influx and intracellular release which were independent of CAMP generation, and 2) membrane depolarization. PTH treatment of fibroblasts depolarized by KCl induced oscillations of [Ca²⁺]_i(but spontaneous oscillatory activity was not observed. Transient elevations of [Ca²⁺]_isimilar to that induced by PTH were observed with PTH-related peptide (PTHrp). PTH regulation of [Ca²⁺]_iwas normal in fibroblasts from patients with pseudohypoparathyroidism (PHP) type Ia (deficiency of the stimulatory GTP-binding protein, G_a), but PTH induced transient decreases in [Ca²⁺]_iin fibroblasts from patients with PHP type Ib (defective PTH receptor). Both PHP Ia and Ib fibroblasts exhibited: 1) spontaneous [Ca²⁺]_ioscilla-tions, possibly due to voltage gated Ca²⁺entry and Ca²⁺induced Ca²⁺release; and 2) greater sensitivity than normal fibroblasts for release of Ca²⁺from intracellular stores when [Ca²⁺]_iwas decreased by lowering external Ca²⁺. Conclusions: 1) PTH- induced transient elevations in [Ca²⁺]_iin normal fibroblasts result from Ca²⁺entry and intracellular release which are independent of CAMP generation; 2) [Ca²⁺]_ihomeostasis is altered in PHP fibroblasts, resulting in Ca²⁺oscillations; 3) PTH regulation of [Ca²⁺]_iis altered in PHP Ib, but not in PHP la fibroblasts.