Calmodulin in the regulation of calcium fluxes in cardiac sarcolemma

Moderation of myocardial ischemia reperfusion injury by calcium channel and calmodulin receptor inhibition

Intracellular Ca2+ accumulation is implicated in the pathogenesis of myocardial reperfusion injury. To study approaches designed to modify Ca2+ uptake during coronary revascularization after acute infarction, a pig heart surgical infarct model (left anterior descending artery occlusion for 60 min) was subjected to 60 min hypothermic potassium cardioplegic arrest, followed by 60 min of global reperfusion. Four groups of six hearts each were studied in a randomized manner, i.e., cardioplegia alone (control), cardioplegia + 10 microM diltiazem (Ca2+ slow channel blocker), cardioplegia + 10 microM trifluoperazine (TFP), (a Ca(2+)-calmodulin antagonist), and cardioplegia+diltiazem (10 microM) + TFP (10 microM). Left ventricular contractility (global and segmental), metabolism (coronary blood flow and O2 consumption), and creatine kinase generation were measured during reperfusion. Both the Ca2+ channel blocker, diltiazem, and the calmodulin antagonist, TFP, improved myocardial global and regional function as well as myocardial metabolism. While diltiazem better restored global and regional contractility, trifluoperazine had a greater effect on coronary blood flow and myocardial oxygen consumption. Enzyme release and lipid peroxidation were equally moderated by both drugs. From this study it can be concluded that Ca2+ influx does play a role in ischemic and reperfusion injury. The mechanisms of its effect are complex, but can be successfully antagonized by Ca2+ blockers as well as by calmodulin antagonists, with improved myocardial preservation.

Cyclic AMP calcium and the growth of mastocytoma cells

Arresting P815 mastocytoma cell growth with N6, O2'-dibutyryladenosine 3':5' cyclic monophosphate (db cAMP) and theophylline increased 45Ca2+ uptake and efflux by the cells (i.e, Ca2+ cycling) without altering cytoplasmic free Ca2+ concentrations or the amount or distribution of protein kinase C in the cells. Attempts to identify the Ca2+ channels involved using a wide variety of drugs were unsuccessful. However, the inhibitory effect of db cAMP on growth was greatly increase in medium containing low Ca2+ concentrations, confirming that interactions between Ca2+ and cyclic AMP can affect mastocytoma cell growth.