Intracellular calcium responses to basic calcium phosphate crystals in fibroblasts.

Area of Science:

• Cell Biology
• Biochemistry
• Crystallography

Background:

• Basic calcium phosphate (BCP) crystals are implicated in various pathological conditions.
• Fibroblast activation and proliferation are crucial processes in tissue repair and disease.
• Intracellular calcium ([Ca2+]i) acts as a vital second messenger in cellular signaling pathways.

Purpose of the Study:

• To investigate the dynamic changes in intracellular calcium levels in fibroblasts upon exposure to BCP crystals.
• To elucidate the sources and mechanisms of BCP-induced calcium signaling in fibroblasts.
• To explore the role of BCP crystal dissolution in modulating fibroblast calcium responses.

Main Methods:

• Fibroblast cultures were treated with BCP crystals.
• Intracellular calcium ([Ca2+]i) was measured using the fura-2 fluorescent dye.
• BCP crystal dissolution was manipulated using ammonium chloride, and extracellular calcium was controlled.
• Proto-oncogene expression was analyzed via Northern blot.

Main Results:

• BCP crystals induced a rapid, 10-fold increase in [Ca2+]i, primarily from extracellular sources.
• A second, sustained rise in [Ca2+]i occurred within 60 minutes, dependent on intracellular crystal dissolution.
• Ammonium chloride significantly inhibited the second [Ca2+]i rise.
• The initial calcium transient was linked to c-fos expression.

Conclusions:

• The initial transient [Ca2+]i increase likely acts as a second messenger for early cellular responses, such as c-fos expression, contributing to BCP-induced mitogenesis.
• The secondary, sustained [Ca2+]i rise is crucial for initiating downstream cellular processes required for fibroblast proliferation.
• Understanding these calcium signaling dynamics is key to deciphering BCP crystal-mediated cellular effects.