Effects of aminoglycoside antibiotics on bound calcium and contraction in guinea‐pig atria

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Abstract
1 We studied the effect of three aminoglycoside antiobiotics which have been shown to replace Ca from lipid monolayers on the superficially bound Ca of isolated beating left atria from guinea-pigs. 2 The cellular Ca content was determined by means of 45Ca after having attained complete exchange. 3 The antibiotics dibekacin, sisomicin, and gentamicin, all reduced the cellular Ca content by 10–20% in a dose-dependent manner. The loss of superficially bound Ca was accompanied by a decline of the contractile force by 40–90%. 4 It is concluded that in isolated atrial muscle it is the amount of Ca bound to the outer surface of the cardiac plasmalemma, rather than the extracellular Ca2+ concentration, that determines contraction height.