Role of ryanodine receptor channels in Ca2+ oscillations of porcine tracheal smooth muscle

Acetylcholine (ACh) induces repetitive, propagating intracellular Ca2+ concentration ([Ca2+](i)) oscillations in porcine tracheal smooth muscle (TSM) cells. Using real-time confocal microscopy, we examined the role of sarcoplasmic reticulum (SR) Ca2+ release through inositol 1,4,5-trisphosphate (IP3) receptor and ryanodine receptor (RyR) channels in ACh-induced [Ca2+](i) oscillations. In beta-escin permeabilized TSM cells, exposure to ACh in the presence of GTP also resulted in [Ca2+](i) oscillations. [Ca2+](i) oscillations could not be initiated by IP3 alone; however, an elevation of [Ca2+](i) was observed. During ongoing [Ca2+](i) oscillations, exposure to heparin, an IP3 receptor antagonist, caused a slowing of oscillation frequency but not complete inhibition. In contrast, ruthenium red, a RyR antagonist, completely abolished ACh-induced [Ca2+](i) oscillations. Reverse transcriptase-polymerase chain reaction of TSM mRNA demonstrated the expression of RyR-2 and RyR-3 isoforms of the RyR. These results indicate that SR Ca2+ release through RyR channels is critical for ACh-induced [Ca2+](i) oscillations in porcine TSM cells.