T‐type Calcium Channels Mediate the Augmented Calcium Influx in Carotid Body Glomus Cells by Chronic Intermittent Hypoxia

Chronic intermittent hypoxia (CIH) is a hallmark manifestation of sleep apnea. In the present study, we examined the effects of CIH on intracellular calcium responses of carotid body glomus cells to acute hypoxia and assessed the underlying mechanisms. Glomus cells were harvested from adult rats, wild‐type and Cav 3.2 null mice treated with 10 days of room air (control) or CIH. Intracellular calcium levels were monitored by single cell imaging with calcium sensitive dye Fura‐2. Hypoxia (pO 2 ~40 mmHg) increased intracellular calcium in glomus cells from control room air treated rats and wild‐type mice, and this response was markedly augmented in CIH treated glomus cells. The augmented intracellular calcium response to CIH was prevented 25μM of TTA‐A2 a specific inhibitor of T‐type calcium channels, in rat glomus cells. Previous studies showed that CaV3.2 is the major T‐type calcium channel in the carotid body glomus cells. Cav 3–2 null glomus cells displayed remarkable absence of augmented calcium response to CIH. Analysis of the underlying mechanisms revealed that CIH had no effect on CaV3.2 mRNA levels in the carotid body. Studies on human embryonic kidney‐293 cells stably expressing CaV3.2 showed that CIH increases CaV3.2 calcium currents and this effect was associated with increased CaV3.2 protein expression in the plasma membrane but not in the cytosol. Either a ROS scavenger or brefeldin‐A, an inhibitor of protein trafficking, prevented the effects of CIH on CaV3.2 currents and the increased protein expression of CaV 3.2 in the plasma membrane. These findings suggest that CIH leads to an augmented calcium influx via ROS‐dependent facilitation of CaV3.2 protein trafficking to the plasma membrane. Support or Funding Information Supported by NIH‐PO1‐HL90554