CaM kinase II and phospholamban contribute to caffeine-induced relaxation of murine gastric fundus smooth muscle

Abstract

Caffeine has been shown to increase the Ca(2+) release frequency (Ca(2+) sparks) from the sarcoplasmic reticulum (SR) through ryanodine-sensitive stores and relax gastric fundus smooth muscle. Increased Ca(2+) store refilling increases the frequency of Ca(2+) release events and store refilling is enhanced by CaM kinase II (CaMKII) phosphorylation of phospholamban (PLB). These findings suggest that transient, localized Ca(2+) release events from the SR may activate CaMKII and contribute to relaxation by enhancing store refilling due to PLB Thr17 phosphorylation. To investigate this possibility, we examined the effects of caffeine on CaMKII, muscle tone, and PLB phosphorylation in murine gastric fundus smooth muscle. Caffeine (1 mM) hyperpolarized and relaxed murine gastric fundus smooth muscle and activated CaMKII. Ryanodine, tetracaine, or cyclopiazonic acid each prevented CaMKII activation and significantly inhibited caffeine-induced relaxation. The large-conductance Ca(2+)-activated K(+) channel blocker iberiotoxin, but not apamin, partially inhibited caffeine-induced relaxation. Caffeine-induced CaMKII activation increased PLB Thr17, but not PLB Ser16 phosphorylation. 3-Isobutyl-1-methylxanthine increased PLB Ser16 phosphorylation, but not PLB Thr17 phosphorylation. The CaMKII inhibitor KN-93 inhibited caffeine-induced relaxation and PLB Thr17 phosphorylation. These results show that caffeine-induced CaMKII activation and PLB phosphorylation play a role in the relaxation of gastric fundus smooth muscles.

Caffeine impairs gastrointestinal function in newborn rats

“…Others have previously shown that ryanodine partially reverses the caffeine relaxant effect in adult rat fundic muscle (15). As shown in Figure 3b, ryanodine reversed the caffeine-induced relaxation by 36% (P < 0.01), an inhibitory effect of similar proportions to the one previously reported in adult rat tissue (15).…”

“…The caffeine effect is not age-dependent such that this compound equally reduces the esophageal and gastrointestinal muscle tone of adult rats. The mechanism responsible for the caffeine-induced gastrointestinal muscle tone in the newborn is mediated via smooth muscle cell ryanodine receptors, as previously shown in adult rat tissue (15). To the best of our knowledge, this is the first English literature report addressing the effect of caffeine on the gastrointestinal muscle tone early in life.…”

“…In adult mice, caffeine decreases the fundal smooth muscle basal tone to ~85% of the response obtained with a nitric oxide donor compound (15). Caffeine also decreases the basal tone and amplitude of phasic smooth muscle contractions in the gastric antrum of adult mice (16).…”

“…Caffeine increases Ca 2+ sparks and spontaneous transient outward currents, in part via ryanodine-sensitive signaling pathways resulting in the relaxation of gastric smooth muscle (12,13). Phospholambaninduced phosphorylation by Ca 2+ /calmodulin-dependent protein kinase II promotes sarcoplasmic reticulum Ca 2+ refilling via ryanodine receptors, further contributing to the caffeine relaxant effect in fundic muscle (15). In adult guinea pigs, caffeine can also induce intestinal smooth muscle relaxation Articles by facilitating the inhibitory responses to isoprenaline, cyclic 3'-5'-adenosine mono-phosphate, and papaverine (18).…”

“…Such data indicate that in adult animals caffeine has a relaxant effect in different smooth muscle types including the gastrointestinal motor fibers (15)(16)(17)(18), via an increase in intracellular cyclic 3' ,5'-adenosine mono-phosphate levels (19)(20)(21), calmodulin kinase II activation (15), and actin depolymerization (22). However, little is known about the caffeine effect on the newborn gastrointestinal function.…”