A multi-parameter approach to measurement of spontaneous myogenic contractions in human stomach: Utilization to assess potential modulators of myogenic contractions

Electrical slow waves, generated by interstitial cells of Cajal (ICC), cause spontaneous contractions of human stomach. Software was developed to measure muscle tone and eleven different parameters defining these contractions in human stomach, displaying data as radar plots. A pilot study assessed the effects of potential modulators, selected from among compounds known to influence ICC activity; n=4-7 each concentration tested/compound. Human distal stomach (corpus-antrum) muscle strips were suspended in tissue baths for measuring myogenic (non-neuronal) contractions in the presence of tetrodotoxin (10-6M). Initial characterization: Contractions (amplitude 4±0.4mN, frequency 3±0.1min-1, n=49) were unchanged by ꭃ-conotoxin GVIA (10-7M) or indomethacin (10-6M) but abolished by nifedipine (10-4M). Carbachol (10-7M) increased contraction rate and amplitude; 10-6-10-5M increased tone and caused large, irregular contractions. [Ca2+]imodulators: Ryanodine (10-5-10-4M) increased muscle tone accompanied by inhibition of myogenic contractions. Xestospongin-C (10-6M; IP3 channel inhibitor) had no effects. SERCA pump inhibitors, 2-APB and cycloplazonic acid (10-5-10-4M) increased tone and myogenic contraction amplitude before abolishing contractions; thapsigargin was weakly active. CaCC blockers: MONNA and CaCCinh-A01 had little-or-no effects on tone but reduced myogenic contractions; MONNA (10-4M) was more effective, reducing amplitude (77.8±15.2%) and frequency. CaV3.1/3.2/3.3 channel block: Mibefradil reduced tone and myogenic contraction amplitude (pIC50 4.8±0.9). Inward-rectifying K+-channel inhibitor: E-4031 (10-4M) increased contraction duration (17.4±5.8%). Conclusions: (1) Measurement of multiple parameters of myogenic contractions identified subtle differences between compounds, (2) only E-4031 and CaCC blockers influenced myogenic contractions, not muscle tone, (3) studies are needed with compounds with known and/or improved selectivity/potency for human targets affecting ICC functions

Copeptin, a surrogate marker of arginine8 vasopressin, has no ability to modulate human and mouse gastric motility.

Copeptin, a glycosylated peptide fragment derived from the C-terminal region of the precursor of arginine8 vasopressin (AVP), is co-secreted with AVP in equimolar amounts. Elevated plasma AVP modulates gastric motility so we investigated whether copeptin had a similar effect. Copeptin (10-9-10-7M), and AVP (10-12-10-5M), were evaluated for their ability to modulate spontaneous and electrically-evoked (EFS) contractions of human proximal and distal gastric circular muscle in vitro. Similar experiments were performed on the mouse stomach and we re-examined the published effect of copeptin on the mouse aorta. In the presence of tetrodotoxin (10-6M), atropine (10-6M) and L-NAME (3 × 10-4M), human proximal and distal stomach muscle contracted spontaneously and rhythmically as did mouse distal stomach. Copeptin (10-9-10-7M), had no effect on baseline muscle tone or myogenic spontaneous contractions of either human or mouse stomach. However, AVP concentration-dependently increased tone, amplitude and frequency of contractions in both regions of human stomach with similar potency (pEC50 9.0-9.5; n = 4) and threshold concentration (10-11-10-10M). AVP was similarly active in the mouse stomach. EFS-evoked cholinergic contractions (human and mouse) were unaffected by both peptides EFS-evoked relaxations of mouse stomach were unaffected by copeptin. In sub-maximally contracted mouse aorta the elevated tone was unaffected by copeptin (10-7M) (cf. previously published study) but was reduced by carbachol (10-6M) and sodium nitroprusside (10-3M). We conclude that in contrast to AVP, copeptin over a concentration range reported in the plasma has no direct ability to modulate the motility of the human and mouse stomach