Ion channelopathies in functional GI disorders

Abstract

In the gastrointestinal (GI) tract, abnormalities in secretion, absorption, motility, and sensation have been implicated in functional gastrointestinal disorders (FGIDs). Ion channels play important roles in all these GI functions. Disruptions of ion channels' ability to conduct ions can lead to diseases called ion channelopathies. Channelopathies can result from changes in ion channel biophysical function or expression due to mutations, posttranslational modification, and accessory protein malfunction. Channelopathies are strongly established in the fields of cardiology and neurology, but ion channelopathies are only beginning to be recognized in gastroenterology. In this review, we describe the state of the emerging field of GI ion channelopathies. Several recent discoveries show that channelopathies result in alterations in GI motility, secretion, and sensation. In the epithelium, mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) or CFTR-associating proteins result in channelopathies with constipation or diarrhea as phenotypes. In the muscle, mutations in the SCN5A-encoded voltage-gated sodium channel Na_V1.5 are associated with irritable bowel syndrome. In the sensory nerves, channelopathies of voltage-gated sodium channels Na_V1.7 and Na_V1.9 (encoded by SCN9A, SCN11A, respectively) manifest by either GI hyper- or hyposensation. Recent advances in structural biology and ion channel biophysics, coupled with personalized medicine, have fueled rapid discoveries of novel channelopathies and direct drug targeting of specific channelopathies. In summary, the emerging field of GI ion channelopathies has significant implications for functional GI disease stratification, diagnosis, and treatment.

Keywords: channelopathy; gastrointestinal; ion channel; mutation.

Fig. 1.

NBCI publications on “channelopathies” since the first publication in 1991 (Accessed on June 8^th, 2016). Solid black line is an exponential fit of the data.

Fig. 2.

IBS-associated SCN5A mutations. Black, no functional abnormalities (6/20, 30%); blue, loss-of-function (13/20, 65%); red, gain-of-function (1/20, 5%).