InsP3, but not novel Ca2+ releasers, contributes to agonist-initiated contraction in rabbit airway smooth muscle

1. To examine the contributions of the putative Ca2+ releasers, inositol 1,4,5-trisphosphate (InsP(3)), cyclic ADP ribose (cADPR), and nicotinate adenine dinucleotide phosphate (NAADP), to carbachol (CCh)-induced contraction in airway smooth muscle, we measured force development of permeabilized rabbit tracheal smooth muscle, human bronchial smooth muscle and guinea-pig ileum longitudinal smooth muscle. 2. In the presence of 50 mu M GTP, CCh and InsP(3) contracted alpha-toxin-permeabilized tracheal smooth muscle dose dependently; the EC50 values for CCh and InsP(3) were 1.84 mu M and 363 mu M, and the maximum responses (normalized to the 30 mM caffeine response) to 100 mu M CCh and to 800 mu M InsP(3) were 206 +/- 13.4% (mean +/- S.E.M.) and 84.4 +/- 5.3%, respectively. 3. However, cADPR (10-300 mu M), beta-NAD(+) (2.5 mM), FK506 (30 mu M) and NAADP (100 mu M) neither contracted the strip by themselves nor affected the subsequent CCh (1 mu M) response. alpha-Toxin-permeabilized bronchial smooth muscle and ileum smooth muscle also responded to caffeine, InsP(3) and CCh but not to cADPR. 4. Both 100 mu M 8-amino-cADPR, a selective cADPR antagonist, and 100 mu M thionicotinamide-NADP, a selective NAADP antagonist, failed to inhibit the CCh response, although procaine abolished the caffeine, InsP(3) and CCh responses in the permeabilized tracheal smooth muscle. 5. Although inhibition of the caffeine response by 30 mu M ryanodine was nearly complete, approximately 30 % of the InsP(3) (300 mu M) plus GTP (50 mu M) response was retained, and the resultant response disappeared after the caffeine response was evoked in the presence of ryanodine. 6. Heparin (300 mu g ml(-1)) blocked InsP(3) (300 mu M) and CCh (3 mu M) responses in beta-escin-permeabilized tracheal smooth muscle, while Ruthenium Red (100 mu M) partially inhibited the CCh response. 7. Collectively, InsP(3) but not cADPR or NAADP plays a key role in CCh-initiated contraction, and InsP(3) utilizes a single compartment of the caffeine/ryanodine-sensitive stored Ca2+ in airway smooth muscle.