NO-mediated regulation of the pacemaker function and motility in the murine jejunum and colon

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NO-sensitive guanylyl cyclase is involved in many physiological regulatory processes such as regulation of blood pressure, synaptic plasticity or gastrointestinal motility. The enzyme is activated by nitric oxide (NO) and catalyzes the formation of the second messenger cGMP. We have generated mice in which NO-GC is deleted globally. These mice suffer from gastrointestinal dysmotility, elevated blood pressure and premature death. However, the cell/tissue types responsible for the individual phenotypes are not yet clear.The reduced GI motility in global GCKO mice is based on the lack of the nitrergic (NO-mediated) relaxation. The exact mechanism of nitrergic relaxation is still not elucidated thoroughly. The identity of the cell types involved in mediating the effect of NO is still unclear as NO-GC is expressed in smooth muscle cells (SMC) as well as interstitial cells of Cajal (ICC), fibroblast-like cells (FLC) and even in certain neurons. Among ICCs, two different subtypes are of special interest with distinct functions: Myenteric ICC (ICC-MY) generate the pacemaker potential whereas intramuscular ICC (ICC-IM) are held responsible of enteric neurotransmission. The effect of neuronally released NO on these two types of ICC is being intensely discussed.In this project, we want to investigate how NO/cGMP regulate rhythmicity of the pacemaker system and spontaneous contractions in different colon and jejunum sections. We will use KO mice lacking NO-GC globally or specifically in SMC, ICC or both. Different parts of jejunum and colon will be taken from these animals for organ bath studies (spontaneous contractions) and microelectrode studies (slow waves). The expression of NO-GC and other members of the NO/cGMP signaling cascade will be investigated using immunohistochemistry. In addition, the ex vivo motility with isolated jejunum and colon from these KO animals will be measured. In all subprojects, we will investigate whether activation of the NO/cGMP system by the novel NO-GC activators/stimulators Bay 41-2272 or Bay 58-26678 (Cinaciguat) have a therapeutic potential with regards to gut motility. Data from murine tissues will finally be correlated to data obtained from human tissues. In summary, our NO-GC KO mice will help to elucidate how slow waves spontaneous contractions are interconnected and regulated by the nitrergic system.