ROLE OF RYANODINE RECEPTOR CHANNELS IN CA2-MUSCLE( OSCILLATIONS OF PORCINE TRACHEAL SMOOTH)

Acetylcholine (ACh) induces repetitive, propagating intracellular Ca2 concentration ([Ca2+](i)) oscillations in porcine tracheal smooth mus cle (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 i n 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 antagoni st, caused a slowing of oscillation frequency but not complete inhibit ion. In contrast, ruthenium red, a RyR antagonist, completely abolishe d ACh-induced [Ca2+](i) oscillations. Reverse transcriptase-polymerase chain reaction of TSM mRNA demonstrated the expression of RyR-2 and R yR-3 isoforms of the RyR. These results indicate that SR Ca2+ release through RyR channels is critical for ACh-induced [Ca2+](i) oscillation s in porcine TSM cells.