D-sotalol was shown to prevent Ca overload and intermyocyte uncoupling. The
aim of this study was to investigate the effect of d-sotalol in Ca paradox
conditions. Guinea pig hearts were perfused at 37 degrees C and constant p
ressure with oxygenated Tyrode solution. Ca paradox was induced by 10 min C
a free perfusion followed by 10 min Ca repletion. 10(-6) M d-sotalol was ad
ministered either during Ca depletion or during Ca repletion period. Electr
ical activity and ventricular contraction were simultaneously recorded and
subcellular alterations were analysed. The contraction terminated in 5 min
of Ca free perfusion and electrical activity disappeared within 5 min of Ca
repletion. Nonuniform injury of myocardial tissue was observed. The majori
ty of cardiomyocytes were irreversibly injured and profound dissociation of
intercellular junctions was detected. Administration of d-sotalol during C
a free period preserved electrical activity and restored ventricular contra
ction accompanied by apparent protection of the ultrastructure, including i
ntercellular connections. Uniform patterns of sarcomeres reflected synchron
ous contraction and protection of junctional couplings. In conclusion, d-so
talol attenuates Ca paradox injury. It seems that the protective effect of
d-sotalol is most likely related to inhibition of potassium efflux antagoni
zing Na loading during Ca depletion period, as well as to attenuation of ex
cess of [Ca2+](i) via acceleration of sarcoplasmic Ca exchange during Ca re
pletion.