Inotrope

The term inotropy ( adjective: inotropic ) refers to the influence on the contractility of muscle tissue. The term is used primarily in the medical field with respect to the cardiac muscle. Drugs that affect the inotropy are called inotropes (singular: inotrope ).

We distinguish the positive inotropic (increase in contractility ) of the negative inotropic ( lowering of contractility ).

Positive inotropy

The positive inotropic effect is generally with an increased provision of calcium ion in the muscle cell in the context. It may be based on different mechanisms:

Binding of catecholamines ( norepinephrine and epinephrine ) in β1 - adrenoceptor activates the G protein signaling cascade - adenylyl cyclase - cAMP calcium ions. Catecholamines thus increasing the contraction amplitude and velocity of contraction increase.

Binding of cardiac glycosides ( such as digoxin, digitoxin and ouabain ) to the α - subunit of sodium potassium ATPase results in inhibition of active transport of potassium ions into the cell and the effluent from the cell of sodium ions. Cytosolic sodium concentration rises and changes the transsarkolemnalen sodium gradient is responsible for the efflux of calcium ions from the cell. The calcium ions thus increasingly taken up into the sarcoplasmic reticulum are thus for the contraction process are available: the force of contraction increases.

Methylxanthines lead via inhibition of phosphodiesterase to increased calcium release and thereby contribute positively inotropic.

Negative inotropic

Especially sympatholytic agents such as beta-blockers have a negative inotropic effect.

The vagus nerve has no particular influence on the contractility of the heart, since it affects only the atrial myocardium and not the ventricles innervated and thus inotropic not significantly negative. ( See article parasympathetic section: heart. )