Calcium-Controlled Secretion Is Effected through a Guanine Nucleotide Regulatory Protein in Parathyroid Cells

Abstract
Calcium regulates parathyroid secretion through mechanisms yet to be elucidated. We have investigated this phenomenon through use of pertussis toxin which catalyzes ADP-ribosylation and inactivation of a guanine nucleotide regulatory protein, possibly Ni or No. Calcium inhibition of PTH release is blocked in cells treated with pertussis toxin, and there is concomitant ADP-ribosylation of a 40-kilodalton protein. The ionophore A23187 inhibits secretion in toxin-treated as well as in control cells. We conclude that a guanine nucleotide regulatory protein is involved in calcium regulation of PTH secretion at a locus proximal to the intracellular site effecting inhibition of secretion.

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