Barium-induced blockade of the inward rectifier in calf Purkinje fibres.
The Ba-induced blockade of iK1 in calf Purkinje fibres was studied in the low concentration range (3-1,000 microM). The results showed that the blockade induced by hyperpolarizations was time-dependent, and that the rate of blockade increased with the Ba concentration and the negative pulse amplitude. At Ba concentrations higher than 1 mM the time course of iK1 blockade was not separable from the capacity transient. At these concentrations, and in a limited voltage range, the Ba-sensitive instantaneous current displayed a marked inward rectification and behaved with external K as expected for a pure K+ current, suggesting that under these conditions the only current affected by Ba was iK1. The Ba-sensitive current deceased with time during hyperpolarizations even when high external K was present, indicating that a voltage-dependent inactivation process could be at least in part responsible for the observed current decline.
D000818:Animals; D001464:Barium / Q000494:pharmacology*; D002417:Cattle; D006329:Heart Conduction System / Q000187:drug effects*; D007473:Ion Channels / Q000187:drug effects*; D011188:Potassium / Q000378:metabolism; D011690:Purkinje Fibers / Q000187:drug effects* / Q000378:metabolism; D013997:Time Factors
D007473:Ion Channels; D001464:Barium; D011188:Potassium