The Journal of General Physiology
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The Journal of General Physiology, Vol 56, 191-217, Copyright © 1970 by The Rockefeller University Press

ARTICLE

Specific Uncoupling of Excitation and Contraction in Mammalian Cardiac Tissue by Lanthanum

Kinetic studies



W. G. Sanborn 1 and G. A. Langer 1

1 From the Department of Physiology and Medicine and the Los Angeles County Cardiovascular Research Laboratory, University of California at Los Angeles, Center for Health Sciences, Los Angeles, California 90024

Arterially cannulated rabbit interventricular septal tissue was exposed to 5–40 µM La in 2.5 mM Ca perfusate. Immediately following perfusion with La two concurrent events were consistently observed: (a) a rapid decline of active tension to a lesser steady-state value, and (b) an abrupt, release of short duration of tissue-bound Ca. The magnitude of both events was directly related to the [La]o. If the duration of exposure to La was brief, contractility returned toward normal upon return to the La-free perfusate. Elevation of [Ca]o during exposure to La counteracted its effect and induced a concurrent displacement of tissue-bound La. Cellular action potentials recorded during brief perfusion with La demonstrated that essentially normal regenerative depolarization was maintained. Analysis of the quantities of 45Ca released following exposure to 10 µM La indicated that this La-susceptible Ca was being displaced from a homogeneous pool—the one previously shown by Langer to represent contractile dependent Ca. These data led to the following conclusions: During perfusion with 2.5 mM Ca contractile dependent Ca was derived primarily from "superficially" located sites. La effected the release of contractile dependent Ca by modifying the normal permselectivity of this "superficial" membrane for activator Ca. These and other data infer that contractile dependent Ca is derived primarily from superficially located sites.

Submitted on July 7, 1969


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G. Nagahashi, W. W. Thomson, and R. T. Leonard
The Casparian Strip as a Barrier to the Movement of Lanthanum in Corn Roots
Science, February 15, 1974; 183(4125): 670 - 671.
[Abstract] [PDF]


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