[Biochemical changes and disorders of electromechanical coupling in chronic heart failure]

In the chronically failing heart, subtle biochemical alterations occur at the level of a number of subcellular systems. The cellular elements that control activation and inactivation of the contractile proteins are the plasma membrane and the sarcoplasmic reticulum (SR). During the plateau phase of the action potential the slow calcium channel is activated so that calcium ions enter into the interior of the cell and initiate--as a trigger signal in loco--the calcium release from the SR-calcium-stores. In the absence of catecholamines the measured calcium ion currents are similar when normal human myocardium is compared to end-stage failing human myocardium. However, the increase in the calcium ion currents induced by maximum concentrations of catecholamines is significantly smaller in failing myocardium compared to normal myocardium. This observation can easily be explained by the down-regulation of the beta-1-adrenoceptors and the increase in the inhibitory Gi-proteins. In the failing myocardium, therefore, a beta-1-adrenoceptor stimulation leads to an insufficient increase in cyclic adenosine monophosphate so that the opening probability of the calcium channels is not appropriately enhanced. This results in a decreased contractile reserve. As far as is known today, the inactivation mechanisms of the plasma membrane (sodium-calcium-exchanger, sodium-potassium ATPase, calcium ATPase) are not disturbed in the failing human myocardium. The calcium release from the SR can be quantified using either calcium indicators (aequorin, fura 2) or highly sensitive thermopiles. Both sophisticated heat measurements and fura-2 measurements indicated a decreased systolic calcium ion concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)