Multiple Ca2+ signaling pathways regulate intracellular Ca2+ activity in human cardiac fibroblasts

Area of Science:

• Cardiovascular Biology
• Cellular Physiology
• Molecular Cardiology

Background:

• Calcium (Ca2+) signaling is extensively studied in cardiac myocytes but remains poorly understood in cardiac fibroblasts.
• Cardiac fibroblasts play crucial roles in cardiac structure and function, particularly during pathological remodeling.

Purpose of the Study:

• To characterize the Ca2+ signaling pathways in cultured human cardiac fibroblasts.
• To investigate the mechanisms underlying spontaneous intracellular Ca2+ (Ca(i)2+) oscillations in these cells.

Main Methods:

• Confocal scanning microscopy was employed to visualize and measure Ca(i)2+ oscillations.
• Reverse transcription polymerase chain reaction (RT-PCR) was used to detect the expression of key Ca2+ handling genes.
• Pharmacological agents were used to probe specific Ca2+ signaling pathways, including store-operated Ca2+ entry, phospholipase C, and IP3 receptors.

Main Results:

• Spontaneous Ca(i)2+ oscillations were observed in a significant portion of human cardiac fibroblasts, with increased frequency upon stimulation.
• These oscillations were dependent on Ca2+ entry and modulated by store-operated Ca2+ channels, phospholipase C, and inositol trisphosphate receptors (IP3Rs), but not ryanodine receptors.
• Gene expression analysis confirmed the presence of mRNAs for IP3Rs, SERCA pumps, CaV1.2 channels, NCX, PMCA, STIM1, and Orai1, but not RyRs.

Conclusions:

• This study reveals the presence of spontaneous Ca(i)2+ oscillations in human cardiac fibroblasts, regulated by distinct pathways compared to cardiomyocytes.
• The findings highlight the involvement of store-operated Ca2+ entry and IP3R-mediated signaling in fibroblast Ca2+ dynamics.
• This research provides a foundational understanding for exploring the role of Ca2+ signaling in fibroblast function and cardiac remodeling.