Inhibition of protein phosphatase 1 decreases PTH secretion from isolated dispersed parathyroid cells

To investigate the regulation of parathyroid hormone secretion by phosphatases we examined the effect of okadaic acid, a selective inhibitor of protein phosphatases (PP)-1 and -2A, on isolated, dispersed parathyroid cells. Okadaic acid inhibited secretion from intact bovine, intact human and streptolysin-O permeabilized bovine cells. Approximately 10(-6) M okadaic acid resulted in a 50% decrease in parathyroid hormone (PTH) secretion from both intact and permeabilized cells, consistent with PP-1 being the target of inhibition. Upon subcellular fractionation, PP-1 overlapped but was not identical to either PTH, a marker of the secretory granule, or Na+/K+-ATPase, a plasma membrane marker. In summary, PP-1 activity is involved in Ca2+-dependent but not basal PTH secretion.