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Multiple effects of calcium antagonists on plateau currents in cardiac Purkinje fibers.

Multiple effects of calcium antagonists on plateau currents in cardiac Purkinje fibers. We studied the influence of Mn, La, and D600 on action potentials and plateau currents in cardiac Purkinje fibers. The Ca antagonists each abolished the second inward current, but they failed to act selectively. Voltage clamp experiments revealed two additional effects: decrease of slow outward current (iotachi) activation, and increase of net outward time-independent plateau current. These effects occurred at inhibitor concentrations used in earlier studies, and were essential to the reconstruction of observed Ca antagonist effects on electrical activity. The inhibitory influence of Mn, La, and D600 on iotachi suggested that iotachi activation might depend upon prior Ca entry. This hypothesis was not supported, however, when Caomicron was varied: elevating Caomicron enhanced Ca entry, but iotachi was nevertheless depressed. Thus, the results suggested instead that Ca antagonists and Ca ions have rather similar effects on iotachi, possibly mediated by changes in membrane surface charge. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png The Journal of General Physiology Rockefeller University Press

Multiple effects of calcium antagonists on plateau currents in cardiac Purkinje fibers.

The Journal of General Physiology , Volume 66 (2): 169 – Aug 1, 1975

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Publisher
Rockefeller University Press
Copyright
© 1975 Rockefeller University Press
ISSN
0022-1295
eISSN
1540-7748
DOI
10.1085/jgp.66.2.169
Publisher site
See Article on Publisher Site

Abstract

We studied the influence of Mn, La, and D600 on action potentials and plateau currents in cardiac Purkinje fibers. The Ca antagonists each abolished the second inward current, but they failed to act selectively. Voltage clamp experiments revealed two additional effects: decrease of slow outward current (iotachi) activation, and increase of net outward time-independent plateau current. These effects occurred at inhibitor concentrations used in earlier studies, and were essential to the reconstruction of observed Ca antagonist effects on electrical activity. The inhibitory influence of Mn, La, and D600 on iotachi suggested that iotachi activation might depend upon prior Ca entry. This hypothesis was not supported, however, when Caomicron was varied: elevating Caomicron enhanced Ca entry, but iotachi was nevertheless depressed. Thus, the results suggested instead that Ca antagonists and Ca ions have rather similar effects on iotachi, possibly mediated by changes in membrane surface charge.

Journal

The Journal of General PhysiologyRockefeller University Press

Published: Aug 1, 1975

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