Single cell [Ca2+](i) studies were performed in chicken and rat osteoclasts loaded with fura-2 and exposed to a variety of treatments. Under resting conditions, basal [Ca2+](i) was 79.2 ± 47.3 and 84.3 ± 65.7 nM (averages ± S.D.; n = 141 and 126) in the osteoclasts of the two species, respectively. Basal [Ca2+](i) was stable in all rat and in ≃80% of chicken osteoclasts. In the remaining 20%, spontaneous, irregular [Ca2+](i) fluctuations were observed (amplitude range: 50-200 nM over basal values). Increase of [Ca2+](o)over the concentration of the Krebs-Ringer incubation medium (2 mM) induced rises of [Ca2+](i) in almost all cells investigated. [Ca2+](i) rises were already appreciable with 0.5 mM [Ca2+](o) additions and reached high values with 4 mM additions: 390 ± 113 and 364 ± 214 nM [Ca2+](i) in rat and chicken osteoclasts, respectively (n = 122 and 101). Qualitatively, the responses to [Ca2+](o) additions consisted of discrete [Ca2+](i) transients, biphasic (an initial spike followed by a plateau), or monophasic (either the spike or the plateau). In a few chicken osteoclasts, the [Ca2+](i) increase occurring after [Ca2+](o) addition consisted of multiple, irregular fluctuations, similar to those observed in 20% of these cells under resting conditions. In individual osteoclasts subsequently exposed to multiple [Ca2+](o) increase pulses, the type of the [Ca2+](i) transient (mono- or biphasic) was maintained, and the size was dependent on the magnitude of the [Ca2+](o) additions. Effects similar to those of [Ca2+](o) were induced by the addition of Cd2+ or Ba2+ (but not La3+ or Mg2+) into the medium. The Cd2+ effect was maintained in part even in a Ca2+-free medium. Of various hormones and factors, parathormone, 1,25-dihydroxyvitamin D3, and prostaglandin E2 were inactive. In contrast, calcitonin was active in rat osteocasts (which express numerous receptors). [Ca2+](i) increases were small (19 ± 17.9 nM; n = 21) when the hormone was administered alone; they were synergistic (severalfold potentiation) when the hormone was administered before or after [Ca2+](o). The [Ca2+](i) effects of calcitonin were mimicked by 8Br-cAMP (31 ± 26 nM; n = 12) when the nucleotide was administered alone; marked synergism when it was administered in combination with [Ca2+](o). This paper demonstrates for the first time that changes of [Ca2+](i) are induced in osteoclasts by treatments with [Ca2+](o) and calcitonin and can therefore be involved in intracellular mediation of the physiological effects of these two extracellular signals.
|Number of pages||6|
|Journal||Journal of Biological Chemistry|
|Publication status||Published - 1989|
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