Non-Selective Cation Channels Mediate Chloroquine-Induced Relaxation in Precontracted Mouse Airway Smooth Muscle

Abstract

Bitter tastants can induce relaxation in precontracted airway smooth muscle by activating big-conductance potassium channels (BKs) or by inactivating voltage-dependent L-type Ca2+ channels (VDLCCs). In this study, a new pathway for bitter tastant-induced relaxation was defined and investigated. We found nifedipine-insensitive and bitter tastant chloroquine-sensitive relaxation in epithelium-denuded mouse tracheal rings (TRs) precontracted with acetylcholine (ACH). In the presence of nifedipine (10 µM), ACH induced cytosolic Ca2+ elevation and cell shortening in single airway smooth muscle cells (ASMCs), and these changes were inhibited by chloroquine. In TRs, ACH triggered a transient contraction under Ca2+-free conditions, and, following a restoration of Ca2+, a strong contraction occurred, which was inhibited by chloroquine. Moreover, the ACH-activated whole-cell and single channel currents of non-selective cation channels (NSCCs) were blocked by chloroquine. Pyrazole 3 (Pyr3), an inhibitor of transient receptor potential C3 (TRPC3) channels, partially inhibited ACH-induced contraction, intracellular Ca2+ elevation, and NSCC currents. These results demonstrate that NSCCs play a role in bitter tastant-induced relaxation in precontracted airway smooth muscle.

Chloroquine Inhibits Ca2+ Signaling in Murine CD4+ Thymocytes

“…In a previous study, we found that bitter-tasting chloroquine can inhibit cytosolic Ca 2+ elevations by blocking TRPC3 channels [25] and VDCCs in mouse airway smooth muscle cells [25,26]. In the present study, we explored whether chloroquine could inhibit Ca 2+ increases in T cells.…”

Taste Receptors Type 2 Would Not Mediate Bitter Tastant-Induced Relaxation of Airway Smooth Muscle

“…However, our and others' results indicate that the relaxation would not be mediated by BKs, which will result from the inhibition of L-type voltage-dependent Ca 2+ channels (LVDCCs) and non-selective cat ion channels (NSCCs) [4][5][6][7]. These studies clarified the paradox about the mechanism of bitter Tastant-induced relaxation.…”

“…However, the agonist ACH-induced the Ca 2+ release from the intracellular store mediated by IP 3 Rs will not be inhibited, thereby, which leads to a depletion of the store to activate SOC (store-operated channels) such as the NSCCs [6]. In addition, ACH (or methacholine) also activates LVDCCs [5,6].…”

“…In addition, ACH (or methacholine) also activates LVDCCs [5,6]. This Ca 2+ per meant ion channels will then mediate Ca 2+ influx, resulting in a sustained contraction.…”

“…This Ca 2+ per meant ion channels will then mediate Ca 2+ influx, resulting in a sustained contraction. If these channels were blocked by bitter tastants, the pre contraction will then be inhibited [5,6].…”