The Role of Hyperpolarization‐Activated Cyclic Nucleotide‐Gated Channels in Ileus Development

Abstract

IntroductionIleus, a decrease or cessation of intestinal contractile activity, affects millions of trauma, post‐operative, and critically ill patients, resulting in longer hospital and ICU stays and increased patient complications. Mechanosensitive ion channels play a role in both the physiological and pathological responses to mechanical stimuli. We found that hyperpolarization‐activated cyclic nucleotide‐gated channel 2 (HCN2) was down‐regulated in edematous intestinal smooth muscle layers. However, the effects of altered HCN channel activity on intestinal contractile activity are largely unknown.ObjectiveThe purpose of the study was to investigate the effects of HCN inhibition on intestinal contractile activity. We hypothesize that inhibition of HCN will decrease intestinal contractile activity. Furthermore, we hypothesize that HCN activity is inhibited by mechanical stretch and/or inflammatory mediator changes that occur during the development of ileus.MethodsThe effects of HCN inhibitors on intestinal contractile activity were investigated ex vivo in an organ bath system. The effects of mechanical stretch, as would occur during the development of ileus, were subsequently examined. The effects of CXCL1, an inflammatory mediator shown to increase in both animal models of ileus and in trauma patients with ileus, were also examined.ResultsHCN inhibition with ZD7288 suppressed agonist‐induced intestinal contractile activity in a dose‐dependent, tetrodotoxin‐resistant manner. Inhibition with an alternative HCN inhibitor, Zatebradine, inhibited agonist‐induced contractile activity in a similar manner. HCN inhibition suppressed calcium sensitivity in the small intestinal. Interestingly, HCN inhibition did not inhibit spontaneous contractile activity. Subjecting intestinal tissue to increased stretch or pretreatment with CXCL1 reduced the effects of ZD7288 on intestinal contractile activity, suggesting that both mechanical stretch and inflammation reduce HCN activity. Preliminary data show that increased intestinal wall stretch decreased HCN protein levels.ConclusionsThe effects of HCN inhibition are tetrodotoxin‐resistant; thus, the effects of HCN inhibition are mediated in the smooth muscle, not the enteric nervous system. Both mechanical stretch and inflammation, which occur during the development of ileus, can inhibit HCN activity. Taken together, these data show that HCN channels are important in agonist‐induced intestinal contractile activity. HCN channels are a novel potential target in the treatment of ileus in post‐operative or critically ill patients.Support or Funding InformationHungarian National Research, Development, and Innovation Office (NKFI 120669) and Institutional Developments for Enhancing Intelligent Specialization Grant (EFOP‐3.6.2‐16‐2017‐0006)