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

UNLABELLED: 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, Gs), 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.