Key result
Calcium removal restores propagated action potentials up to ~74 mV and suppresses contracture in SAN cells.
Why the study?
The effects of extreme extracellular calcium reduction on sino-atrial node cells treated with potassium-depleted solutions were not well understood.
In rabbit sino-atrial node cells exposed to potassium-free media, extreme extracellular calcium reduction decreases intracellular calcium overload and increases action potential amplitude.
May alleviate calcium overload in sinoatrial node cells during potassium depletion; leaves open applicability to human electrophysiology.
The effect of extreme calcium reduction was studied in rabbit sino-atrial node cells treated with K-free media. Ca removal (Ca = 0, EGTA = 6 mM) suppressed spontaneous miniature fluctuations elicited by exposure to the K-free media. Further, successive exposure to the Ca-free, EGTA solutions produced a propagated action potential and suppressed a contracture. The action potential was not noticeably altered by tetrodotoxin (TTX). In the presence of normal Ko, reducing the bathing calcium concentration with EGTA prolonged the duration of the action potential. The potential induced by Ca removal was similar to that observed in the K-free media. From these results, we have concluded that a drastic reduction in the extracellular Ca concentration produces a decrease in the overloaded Ca in the cell exposed to the K-free media, resulting in an increase in the amplitude of action potentials.
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Miyamae et al. (1986) studied Sino-atrial node cells treated with potassium-depleted solutions. Extracellular calcium removal (Ca-free, 6 mM EGTA solution) vs. K-free media without Ca removal was evaluated on Amplitude of propagated action potentials. In rabbit sino-atrial node cells treated with potassium-free media, removal of extracellular calcium produced a propagated action potential with a maximum amplitude of 74±2 mV and suppressed contracture.
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