A K-ATP CHANNEL OPENER PROTECTS CARDIOMYOCYTES FROM CA2- A LASER CONFOCAL MICROSCOPY STUDY( WAVES )

Laser confocal microscopy was used to visualize intracellular spatiote mporal Ca2+ patterns in single guinea pig ventricular myocytes loaded with the Ca2+ indicator, fluo 3-acetoxymethyl ester (flue 3-AM), and e xposed to moderately elevated extracellular K+ to induce partial membr ane depolarization. Analysis of K+-induced intracellular Ca2+ elevatio n revealed three distinct paradigms: 1) diffuse, nonoscillatory Ca2+ e levation across the myocyte; 2) localized Ca2+ elevation in anatomical ly restricted areas (Ca2+ sparks); and 3) regenerative frontal propaga tions of Ca2+ that traversed the length of the cell (Ca2+ waves). The first two patterns were more frequently observed when the extracellula r K+ concentration was raised to 8 mM. Ca2+ waves became more common w hen extracellular K+ concentration was increased to 16 mill, suggestin g that a minimum threshold of increase in intracellular Ca2+ is necess ary for the organization of Ca2+ waves. The velocity of propagation wa s typically similar to 60 mu m/s with an average frequency of one wave per second crossing at a given point in the cell. Wave propagation re sulted in spatial and temporal oscillations in cytosolic and nuclear C a2+ concentration. Treating cardiac cells with aprikalim, a potassium channel-opening drug, prevented 16 mM K+ (but not 32 mM K+) from induc ing an increase in Ca2+ concentration and from generating Ca2+ waves. In cardiomyocytes treated with glyburide, a selective antagonist of AT P-sensitive K+ channels, aprikalim failed to prevent 16 mM K+ from ind ucing Ca2+ waves. In summary, moderate hyperkalemia induces distinct n onuniform patterns of intracellular Ca2+ elevation in ventricular cell s, which can be prevented by a potassium channel-opening drug through a glyburide-sensitive mechanism.