Cytosolic Ca2+ and the regulation of secretion in parathyroid cells.

The concentration of intracellular Ca2+ [( Ca2+]i) was measured in dissociated bovine parathyroid cells loaded with quin-2 or fura-2. In quin-2-loaded cells, increases in the concentration of extracellular Ca2+ elicited slow, monophasic increases in [Ca2+]i, whereas in fura-2-loaded cells, extracellular Ca2+ evoked rapid, transient increases which were followed by lower, yet sustained increases in [Ca2+]i. Cytosolic Ca2+ transients arose from the mobilization of cellular Ca2+ and could be evoked by a variety of divalent cations. Transient, but not sustained increases in [Ca2+]i were associated with an inhibition of hormone secretion. Secretion was still inhibited, however, when cytosolic Ca2+ transients were blocked by buffering with quin-2, suggesting that changes in [Ca2+]i might not be the essential factor regulating secretion in parathyroid cells.