Search

The activation of M3 cholinoceptors (M3 receptors) by choline reduces cardiovascular risk, but it is unclear whether these receptors can regulate ischaemia/reperfusion (I/R)-induced vascular injury. Thus, the primary goal of the present study was to explore the effects of choline on the function of mesenteric arteries following I/R, with a major focus on Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) regulation.Rats were given choline (10 mg · kg(-1), i.v.) and then the superior mesenteric artery was occluded for 60 min (ischaemia), followed by 90 min of reperfusion. The M3 receptor antagonist, 4-diphenylacetoxy-N-methylpiperidine methiodide (4-DAMP), was injected (0.12 μg · kg(-1), i.v.) 5 min prior to choline treatment. Vascular function was examined in rings of mesenteric arteries isolated after the reperfusion procedure. Vascular superoxide anion production, CaMKII and the levels of Ca(2+)-cycling proteins were also assessed.Choline treatment attenuated I/R-induced vascular dysfunction, blocked elevations in the levels of reactive oxygen species (ROS) and decreased the up-regulated expression of oxidised CaMKII and phosphorylated CaMKII. In addition, choline reversed the abnormal expression of Ca(2+)-cycling proteins, including Na(+)Ca(2+) exchanger, inositol 1,4,5-trisphosphate receptor, sarcoplasmic reticulum Ca(2+)-ATPase and phospholamban. All of these cholinergic effects of choline were abolished by 4-DAMP.Our data suggest that inhibition of the ROS-mediated CaMKII pathway and modulation of Ca(2+)-cycling proteins may be novel mechanisms underlying choline-induced vascular protection. These results represent a significant addition to the understanding of the pharmacological roles of M3 receptors in the vasculature, providing a new therapeutic strategy for I/R-induced vascular injury.

Using whole-cell patch clamp technique this study investigated the effects of adenosine (Ado) on action potential, L-type calcium current (I(Ca.L)), delayed afterdepolarizations (DADs), and transient inward current (I(ti)) induced by isoproterenol (Iso) in guinea pig isolated single ventricular myocytes. The results showed: (1) Ado alone had no significant direct effects on action potential and I(Ca.L) in guinea pig ventricular myocytes at 20-100 micromol/L. However, Ado significantly attenuated the prolongation of action potential duration (APD) and the increase of the peak amplitude of I(Ca.L) induced by Iso. Iso (10 nmol/L) markedly increased APD(50) and APD(90) from 340+/-21 ms to 486+/-28 ms and from 361+/-17 ms to 501+/-29 ms, respectively (P0.01), and increased the amplitude of I(Ca.L) from 6.53+/-1.4 pA/pF to 18.28+/-2.4 pA/pF (P0.01). The peak potential of current-potential relationship shifted to the left. Ado (50 micromol/L) abbreviated APD(50), APD(90) to 403+/-19 ms and 419+/-26 ms (P0.01), and decreased the peak amplitude of I(Ca.L) to 10.2+/-1.5 pA/pF (P0.01 vs Iso), but did not change resting membrane potential (RMP), action potential amplitude (APA), and overshoot (OS). (2) Iso (30 nmol/L) reproducibly elicited DADs with 100% incidence of DADs under this condition. Ado (50 micromol/L) completely inhibited Iso from inducing DADs. Iso (30 nmol/L) elicited I(ti) with 2-second depolarizing voltage-clamp pulses rising to +20 mV from a holding potential of -40 mV, the incidence of I(ti) being 100%, and the I(ti) was suppressed in the presence of Ado (50 micromol/L) with the incidence of I(ti) decreased to 14.3% (P0.05). These data indicate that Ado antagonizes the stimulatory effect of Iso, and that the antiarrhythmic mechanism of Ado preventing Iso-induced DADs is due to the inhibition of intracellular Ca(2+) overload through attenuating the prolongation of APD, the enhance of I(Ca.L) and I(ti).