Calcium transport in isolated bone cells III. Effects of parathyroid hormone and cyclic 3′, 5′-AMP

The effects of parathyroid hormone(PTH) and cyclic 32, 52-AMP (cyclic AMP) on calciumtransport were studied in isolated bone cells.Bone cells were isolated by collagenase digestionof 20—21 day old fetal rat calvaria. Calciumtransport was measured with 45Ca. PTH (0.2 μg/ml)increased calcium uptake 30—40% over control valuesat 37 C. At 4 C, the effects were magnified and70—170% increases in calcium uptake were observed.The effects were present 1—10 minutes afterthe simultaneous addition of hormone and 45Ca.PTH had no effect on calcium efflux. Neitherdibutyryl cyclic AMP (10^-4-10^-3M) nor cyclic AMP(10^-7—3 × 10^-6M) had any effect on calcium uptake orefflux. Methylisobutylxanthine (0.1 mM) caused nochange in calcium uptake although increases incyclic AMP were noted. The characteristic PTHinducedincrease in cyclic AMP seen at 37 C wasnot observed at 4 C. It is postulated that PTH increases the permeabilityof bone cell membranes to calcium. At 4 Cthe membrane is relatively impermeable so the PTHeffect is magnified. The PTH-induced increasedoes not appear to be mediated through cyclicAMP.