Effect of calmodulin antagonists on hypoxia and reoxygenation damage in isolated rabbit hearts

Anti-ischemic and membrane stabilizing activity of calmodulin inhibitors

In the control perfused working rat hearts subjected to 25 min global ischemia, reperfusion resulted in a 50% recovery of the hemodynamic functions. A concentration-dependent improvement of this recovery and a reduction of the postischemic lactate dehydrogenase (LDH) release was caused by calmidazolium (CMZ), trifluoperazine (TFP), and chlorpromazine (CPZ) added prior to ischemia. The drugs were not effective when added only to the reperfusate. The concentrations of CMZ, TFP, and CPZ producing the half-maximal effects were 2.5 X 10(-9) M, 1.5 X 10(-7) M and 3 X 10(-7) M, respectively. Prolongation of the ischemic period caused a progressive deterioration of the functional recovery of the hearts while the total postischemic LDH release showed, at the same time, an initial gradual rise followed by a later decay. In untreated hearts the duration of ischemia resulting in 50% loss of hemodynamic function and in a maximal LDH release was 25 min. TFP (10(-6) M) and CMZ (10(-7) M) prolonged these times by 4-7 min and 5-10 min. respectively. TFP, CPZ, and CMZ protected the erythrocytes from osmotic hemolysis. The maximum anti-hemolytic activity was produced by 3 X 10(-6) M CMZ, 3 X 10(-5) M TFP, and 10(-4) CPZ. The concentration-dependency of this effect was not affected by low concentrations of sodium dodecyl sulphate (SDS). Neither TFP nor CMZ prevented the hemolysis produced by 10(-3) M SDS. It is concluded that the delay in the development of the ischemic injury produced by TFP and CMZ is due to the effects of these drugs as calmodulin antagonists rather than as membrane stabilizers.

New anti-ischaemic drugs: cytoprotective action with no primary haemodynamic effects

Currently therapy for ischaemic heart disease is based on drugs such as beta-adrenoceptor antagonists, Ca2+ antagonists and nitrates, which have pronounced haemodynamic effects. However, these drugs can have adverse reactions including systemic haemodynamic effects, leading to low blood pressure and peripheral oedema in some patients. Recent observations that certain types of Ca2+ antagonist prevent the Ca2+ overload that occurs after ischaemia have led to the design of new anti-ischaemic drugs that are cytoprotective, but have no (or few) haemodynamic effects. In this article, Pieter van Zwieten and colleagues assess the therapeutic potential of these drugs.

Amiodarone is a potent calmodulin antagonist

The possible interaction between amiodarone, a potent antiarrhythmic and antianginal agent, and calmodulin (CaM) was investigated by three avenues of approach: (a) Effect of amiodarone on cardiac and vascular Ca2+/calmodulin-activated cyclic nucleotide phosphodiesterase (CaM-PDE); (b) Effect on the CaM-activated (Ca2+ + Mg2+)-ATPase from human erythrocytes; (c) Direct interaction between amiodarone and calmodulin measured by the effect of the drug on the fluorescence of 9-anthroylcholine (9AC) bound to calmodulin. Results show that amiodarone did not interact with basal activities of CaM-PDE and other isolated CaM-insensitive PDE forms as well as with (Ca2+ + Mg2+)-ATPase. Amiodarone inhibited calmodulin-activation of aortic CaM-PDE (Ki = 650 nM, substrate cGMP) and calmodulin-activation of erythrocyte ghosts (Ca2+ + Mg2+)-ATPase (IC50 = 4.5 microM) in an apparently competitive manner. Amiodarone decreased the fluorescence of the hydrophobic probe 9AC bound to calmodulin (IC50 = 5 microM). It is concluded that amiodarone is a potent calmodulin antagonist.