Potassium and insulin affect the contractility of abomasal smooth muscle

Abomasal displacement is a frequent and important disease of high yielding dairy cows. Although several factors are related to its occurrence, the pathogenesis of the condition is still inadequately understood, particularly in regard to K+ and insulin homeostasis. For this reason the aim was to investigate the effects of K+ and insulin concentrations on in vitro motility of abomasal smooth muscle. The second aim was to determine whether the in vivo change in K+ and insulin levels might be sufficient to induce reduced abomasal motility. Muscle strips were isolated from the abomasum of slaughtered cows and incubated in buffer solution under isometric conditions. Results show that a decrease in extracellular K+ (between 5 and 1 mmol/L) or an increase in extracellular insulin concentrations (to 21 mU/L or higher) were able to affect the contraction activity of abomasal muscles. Contraction activity given as median (25th, 75th percentiles) changed from 28.1 mN/min (2.5, 49.9) at 5 mmol/L of K+ to 9.4 mN/min (0.6, 35.7) at 1 mmol/L of K+, and from 34.5 mN/min (10.8, 112.4) at 0 mU/L of insulin to 12.0 mN/min (7.6, 49.8) at 120 mU/L of insulin. Because the effect of insulin could be abolished by barium, glybenclamide, or ouabain, the underlying mechanisms of the insulin action could be an increased K+ conductance or an increased Na/K-ATPase activity or both. Low K+ or high insulin concentrations both reduced the activity of the circular muscle of the abomasal corpus (i.e., of the part that is responsible for the propulsion of abomasal chymus) and might play an important role in the pathogenesis of abomasal displacement.