Ranolazine inhibits voltage-gated mechanosensitive sodium channels in human colon circular smooth muscle cells

Am J Physiol Gastrointest Liver Physiol. 2015 Sep 15;309(6):G506-12. doi: 10.1152/ajpgi.00051.2015. Epub 2015 Jul 16.

Abstract

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.

Keywords: SCN5A; colon; ranolazine; smooth muscle; sodium channel.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Colon / drug effects
  • Colon / metabolism*
  • Colon, Ascending / drug effects
  • Colon, Ascending / metabolism
  • Constipation / genetics
  • HEK293 Cells
  • Humans
  • Muscle Contraction / physiology
  • Myocytes, Smooth Muscle / drug effects
  • Myocytes, Smooth Muscle / metabolism*
  • NAV1.5 Voltage-Gated Sodium Channel / genetics
  • NAV1.5 Voltage-Gated Sodium Channel / metabolism
  • Patch-Clamp Techniques
  • Physical Stimulation
  • Potassium Channel Blockers / pharmacology*
  • Potassium Channels, Voltage-Gated / drug effects*
  • Ranolazine / pharmacology*

Substances

  • NAV1.5 Voltage-Gated Sodium Channel
  • Potassium Channel Blockers
  • Potassium Channels, Voltage-Gated
  • SCN5A protein, human
  • Ranolazine