Catecholamines include adrenaline, noradrenaline and dopamine. They are physiologically important neurotransmitters, as part of the sympathetic and central nervous systems. Catecholamines act on both the alpha and beta adrenergic receptors. Catecholamines are released in times of stress. They make your heart beat faster with greater force and narrow the blood vessels, causing a rise in blood pressure. The beta1 effects of catecholamine on the heart are due to an increase in intracellular concentration of cyclic-AMP. Cyclic-AMP activates protein kinase A, which phosphorylates sites on calcium channels, including alpha1-subunits. This increases the probability that the channels will open, increasing inward calcium ion current and therefore the force of cardiac contraction. It also increases the calcium ion capture by the sarcoplasmic reticulum, increasing the amount of calcium stored intracellularly available for release by action potential. So the net result of catecholamine action is to elevate and steepen the ventricular function curve. The increase in heart rate results in an increased slope of pacemaker potential owing to a shift in the voltage-dependence of the conductance's underlying the pacemaker currents so that they are switched on and reach firing threshold, earlier.