The relative contribution of inositol 1,4,5-trisphosphate receptors (IP₃Rs) and ryanodine receptors (RyRs) to agonist-induced Ca²⁺ signaling in mouse airway SMCs was investigated in lung slices with phase-contrast or laser scanning microscopy. At room temperature, methacholine (MCh) or 5-hydroxytryptamine (5-HT) induced Ca²⁺ oscillations and an associated contraction in small airway smooth muscle cells (SMCs). The subsequent exposure to an IP₃R antagonist, 2-aminoethoxydiphenyl borate (2-APB), inhibited the Ca²⁺ oscillations and induced airway relaxation in a concentration-dependent manner. 2-APB also inhibited Ca²⁺ waves generated by the photolytic release of IP₃. However, the RyR antagonist ryanodine had no significant effect, at any concentration, on airway contraction or agonist- or IP₃-induced Ca²⁺ oscillations or Ca²⁺ wave propagation. By contrast, a second RyR antagonist, tetracaine, relaxed agonist-contracted airways and inhibited agonist-induced Ca²⁺ oscillations in a concentration dependent manner. However, tetracaine did not affect IP₃-induced Ca²⁺ release or wave propagation nor the Ca²⁺ content of SMC Ca²⁺ stores as evaluated by Ca²⁺-release induced by caffeine. Conversely, both ryanodine and tetracaine completely blocked agonist-independent slow Ca²⁺ oscillations induced by KCl. The inhibitory effects of 2-APB and absence of an effect of ryanodine on MCh-induced airway contraction or Ca²⁺ oscillations of SMCs were also observed at 37^oC. In Ca²⁺-permeable SMCs, tetracaine inhibited agonist-induced contraction without affecting intracellular Ca²⁺ levels indicating that relaxation also resulted from a reduction in Ca²⁺ sensitivity. These results indicate that agonist-induced Ca²⁺ oscillations in mouse small airway SMCs are primary mediated via IP₃Rs and that tetracaine induces relaxation by both decreasing Ca²⁺ sensitivity and inhibiting agonist-induced Ca²⁺ oscillations via an IP₃-dependent mechanism.