Enhancement of cardiac actions of ouabain and its binding to Na+, K+-adenosine triphosphatase by increased sodium influx in isolated guinea-pig heart.

摘要: The rate of development the positive inotropic action ouabain is enhanced when heart stimulated at higher frequencies. A hypothesis that this enhancement due to a stimulation glycoside binding sarcolemmal Na+,K+-adenosine triphosphatase (ATPase) caused by an increase in intracellular Na+ available sodium pump was tested isolated left atrial muscle preparations guinea-pig heart, incubated 30 degrees C and electrically 0.5, 1 or 2 Hz. dependent on frequency stimulation. Each preparation homogenized predetermined time fractional occupancy Na+,K+-ATPase estimated from decrease initial velocity ATP-dependent [3H]ouabain reaction. parallel relationship observed between effects those ouabain. In quiescent preparations, ionophore, monensin, contracture toxic concentration also Na+,K+-ATPase. Similar ouabain-induced were with either grayanotoxin I batrachotoxin, agents known influx, exposed these under 1.5 Hz subsequently for actions quiescence. When exposure batrachotoxin restricted period, not significantly altered. Monensin, failed affect homogenates added medium labeled assay. These results indicate ions promote thereby enhance heart. "beat-dependent" onset least partially explained effect membrane depolarization binding.