Presenting Author:

Lindsay Forbes, M.D.

Principal Investigator:

Jacob Sznajder, M.D.

Department:

Medicine

Keywords:

SERCA, MCU, calcium, airway smooth muscle cells, hypercapnia

Location:

Third Floor, Feinberg Pavilion, Northwestern Memorial Hospital

B78 - Basic Science

Mechanism of Calcium Increase in Hypercapnic Airway Smooth Muscle Cells

Introduction: Intracellular calcium (Ca) concentration is increased in lung cells including airway smooth muscle cells (ASMC) in hypercapnic conditions. Increased intracellular Ca causes a cascade of cellular events which result in ASMC contraction. ASMC contraction has been implicated in disease states such as asthma, bronchitis and emphysema. This project examines the mechanism of intracellular Ca increase in hypercapnia. Specifically, it looks at the mitochondrial calcium uniporter (MCU) and sarcoendoplasmic reticulum calcium transport ATPase (SERCA). Both are responsible for Ca uptake into their respective organelles, and therefore decreased expression of either may explain the increased intracellular Ca concentration. Methods: ASMC were exposed to either normocapnic (5% CO2) or hypercapnic (20% CO2, pH 7.4) conditions for 6 hours, 12 hours, or 2 days. Protein expression of MCU and SERCA was measured via Western blot. Additionally, gene expression of MCU was measured via qPCR. Results were analyzed using GraphPad Prism software; statistical significance was assessed with one-way ANOVA. When differences found by ANOVA were statistically significant, further testing to account for multiple comparisons was performed by Dunnett’s test. Results: SERCA protein levels trended towards an increase in hypercapnic conditions at 6 and 12 hours but not at 2 days. MCU protein levels were not significantly in different in normocapnic and hypercapnic conditions at 6 hours, 12 hours and 2 days. However, MCU gene expression was significantly increased in hypercapnic conditions at 6 hours (p=0.0136) but not at 12 hours and 2 days. Conclusions: This study suggests that an alternative mechanism is responsible for the observed Ca increase during hypercapnia. Such mechanisms might include posttranslational modification leading to decreased function of either MCU or SERCA or a change in alternative cell proteins involved in intracellular Ca metabolism.