Regulation of cytosolic calcium by parathyroid hormone and oscillations of cytosolic calcium in fibroblasts from normal and pseudohypoparathyroid patients

The second messengers for PTH action on fibroblasts 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 human dermal skin fibroblasts. PTH induced: 1) transient elevations of [Ca²⁺]_i due 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⁺]_i similar to that induced by PTH were observed with PTH-related peptide (PTHrp). PTH regulation of [Ca²⁺]_i was normal in fibroblasts from patients with pseudohypoparathyroidism (PHP) type Ia (deficiency of the stimulatory GTP-binding protein, G_s), but PTH induced transient decreases in [Ca²⁺]_i in fibroblasts from patients with PHP type Ib (defective PTH receptor). Both PHP Ia and Ib fibroblasts exhibited: 1) spontaneous [Ca²⁺]_i oscillations, 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⁺]_i was decreased by lowering external Ca²⁺. Conclusions: 1) PTH-induced transient elevations in [Ca²⁺]_i in normal fibroblasts result from Ca²⁺ entry and intracellular release which are independent of CAMP generation; 2) [Ca²⁺]_i homeostasis is altered in PHP fibroblasts, resulting in Ca²⁺ oscillations; 3) PTH regulation of [Ca²⁺]_i is altered in PHP Ib, but not in PHP Ia fibroblasts.