α1-Adrenergic receptor regulates papillary muscle and aortic segment contractile function via modulation of store-operated Ca entry in long-tailed ground squirrels Urocitellus undulatus.

The effect of phenylephrine (PE) on right ventricle papillary muscle (PM) and aortic segment (AS) contractile activity was studied in long-tailed ground squirrels Urocitellus undulatus during summer activity, torpor and interbout active (IBA) periods in comparison to rat. We found that PE (10 μM) exerts positive inotropic effect on ground squirrel PM that was blocked by α1-AR inhibitor-prazosin. PE differently affected frequency dependence of PM contraction in ground squirrels and rats.

Calmodulin-dependent regulation of calcium-activated outward current in frog atrial membrane.

The steady-state outward current underlying the inward-going rectification in frog atrial fibers has been studied by the double sucrose gap technique. Similar to the case in sheep Purkinje fibers (18,19), the inward rectifying potassium channels in frog atrium are blocked by cesium (5 mM) and activated by increasing cytosolic calcium concentration (replacing 30% of the Na by sucrose). It was shown that trifluoperazine (5 x 10(-6) M), a widely used blocker of the Ca-calmodulin complex, inhibits the inward rectifying potassium channels.