Rhee, Poong‐Lyul

Human jejunum smooth muscle cells (SMCs) and interstitial cells of Cajal (ICCs) express the SCN5A-encoded voltage-gated, mechanosensitive sodium channel NaV1.5. NaV1.5 contributes to small bowel excitability, and NaV1.5 inhibitor ranolazine produces constipation by an unknown mechanism. We aimed to determine the presence and molecular identity of Na+ current in the human colon smooth muscle and to examine the effects of ranolazine on Na+ current, mechanosensitivity, and smooth muscle contractility. Inward currents were recorded by whole cell voltage clamp from freshly dissociated human colon SMCs at rest and with shear stress. SCN5A mRNA and NaV1.5 protein were examined by RT-PCR and Western blots, respectively. Ascending human colon strip contractility was examined in a muscle bath preparation. SCN5A mRNA and NaV1.5 protein were identified in human colon circular muscle. Freshly dissociated human colon SMCs had Na+ currents (−1.36 ± 0.36 pA/pF), shear stress increased Na+ peaks by 17.8 ± 1.8% and accelerated the time to peak activation by 0.7 ± 0.3 ms. Ranolazine (50 μM) blocked peak Na+ current by 43.2 ± 9.3% and inhibited shear sensitivity by 25.2 ± 3.2%. In human ascending colon strips, ranolazine decreased resting tension (31%), reduced the frequency of spontaneous events (68%), and decreased the response to smooth muscle electrical field stimulation (61%). In conclusion, SCN5A-encoded NaV1.5 is found in human colonic circular smooth muscle. Ranolazine blocks both peak amplitude and mechanosensitivity of Na+ current in human colon SMCs and decreases contractility of human colon muscle strips. Our data provide a likely mechanistic explanation for constipation induced by ranolazine.

Abstract Background There is little information regarding gender‐specific measurements of colonic transit and anorectal function in patients with defecation disorders ( DD ). To compare overall colonic transit by gender in DD . Methods In 407 patients with constipation due to DD diagnosed by a single gastroenterologist (1994–2012), DD was characterized by anorectal manometry, balloon expulsion test, and colonic transit by scintigraphy. The primary endpoint was overall colonic transit (geometric center, GC ) at 24 h ( GC 24). Effects of gender in DD on colonic transit, and comparison with transit in 208 healthy controls were assessed by Mann–Whitney rank sum test. Secondary endpoints were maximum anal resting ( ARP ) and squeeze ( ASP ) pressures. We also tested association of the physiological endpoints among DD females by pregnancy history and among DD patients by colectomy history. Key Results The DD patients were 67 males (M) and 340 females (F). Significant differences by gender in DD patients were observed in GC 24 (median: M: 2.2; F: 1.8; P = 0.01), ARP (median: M: 87.8 mmHg; F: 82.4 mmHg; P = 0.04), and ASP (median: M: 182.4 mmHg; F: 128.7 mmHg; P < 0.001). GC 24 was slower in DD compared with same‐gender healthy controls. GC 24 did not differ among DD females by pregnancy history. Anorectal functions and upper GI transit did not differ among DD patients by colectomy history. Conclusions & Inferences Patients with DD have slower colonic transit compared with gender‐matched controls. Among DD patients, males have higher ARP and ASP , and females have slower colonic transit. Although the clinical significance of these differences may be unclear, findings suggest that interpretation of these tests in suspected DD should be based on same‐gender control data.