Control of cytosolic free calcium in rat and chicken osteoclasts. The role of extracellular calcium and calcitonin.
Single cell [Ca2+], 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 approximately 80% of chicken osteoclasts. In the remaining 20%, spontaneous, irregular [Ca2+], 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+] in almost all cells investigated. [Ca2+] 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+], 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 osteoclasts (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.
Malgaroli
A
A
Institute of Human Anatomy, University of Bari, Italy.
Meldolesi
J
J
Zallone
A Z
AZ
Teti
A
A
D000818:Animals; D001572:Benzofurans; D002104:Cadmium; D002116:Calcitonin / Q000502:physiology*; D002118:Calcium / Q000378:metabolism* / Q000502:physiology; D002645:Chickens; D006152:Cyclic GMP / Q000031:analogs & derivatives / Q000494:pharmacology; D003600:Cytosol / Q000378:metabolism* / Q000502:physiology; D004357:Drug Synergism; D005110:Extracellular Space / Q000378:metabolism / Q000502:physiology*; D005260:Female; D016257:Fura-2 / Q000031:analogs & derivatives*; D006728:Hormones / Q000494:pharmacology; D007811:Lanthanum; D008274:Magnesium; D010010:Osteoclasts / Q000378:metabolism / Q000502:physiology*; D051381:Rats; D011919:Rats, Inbred Strains
D001572:Benzofurans; D006728:Hormones; D002104:Cadmium; C049925:fura-2-am; C016276:8-bromocyclic GMP; D007811:Lanthanum; D002116:Calcitonin; D006152:Cyclic GMP; D008274:Magnesium; D002118:Calcium; D016257:Fura-2