| Intracellular signal transduction involves multiple interactions between signaling molecules. For efficient signal transduction, signaling components are spatially organized into complexes by scaffolding proteins. Among these is caveolin-1, identified in 1998 as the structural protein component of the plasma membrane caveolae. These are flask-shaped invaginations that were later shown to be enriched in a number of signaling proteins whose function is regulated by caveolin-1. The roles of caveolin-1 in the regulation of signaling pathways that control small intestinal motility are currently unknown. In this thesis, I used caveolin-1 knockout mice to elucidate the role of caveolin-1 in the regulation of some signaling pathways in mouse small intestine.;Another pathway leading to intestinal smooth muscle relaxation was also affected by caveolin-1 loss. cAMP-dependent relaxation downstream of beta-adrenoceptor stimulation was reduced in caveolin-1 knockout mice compared to their wild type controls. I showed that this reduction was likely due to the redistribution of the downstream mediator of cAMP relaxation, protein kinase A, away from its downstream targets.;Furthermore, wild type mice expressed a splice variant of neuronal nitric oxide synthase in small intestinal smooth muscle. This was activated in response to calcium entry into smooth muscle cells to produce nitric oxide that counteracted the contraction. The caveolin-1 knockout tissues lacked this splice variant and the effect it exerts on smooth muscle contraction.;Finally, I found that calcium extrusion from intestinal smooth muscle through the plasma membrane calcium ATPase isoform 4 was reduced in caveolin-1 knockout mice. This was probably due to the loss of the close association between the plasma membrane and the sarcoplasmic reticulum at the caveolae domains. To conclude, my observations suggest that the alteration in the examined functions due to the loss of caveolin-1 is likely a result of the loss of organization of key signaling molecules closely related to caveolae.;First, I examined how the nitric oxide-mediated relaxation changed in caveolin-1 knockout mouse small intestine. This tissue showed reduced relaxation to endogenous and exogenous nitric oxide. I showed that this reduction was due to an increased activity of phosphodiesterase 5, which metabolizes cGMP, a mediator of nitric oxide effects. |
