Abstract
Ca2+ release from the sarcoplasmic reticulum (SR) of mammalian cardiac myocytes occuring either due to activation by a depolarization or the resulting transmembrane Ca2+ current (I Ca), or spontaneously due to Ca2+ overload has been shown to cause inward current(s) at negative membrane potentials. In this study, the effects of different intracellular Ca2+ chelating compounds on I Ca-evoked or spontaneous Ca2+-release-dependent inward currents were examined in dialysed atrial myocytes from hearts of adult guinea-pigs by means of whole-cell voltage-clamp. As compared to dialysis with solutions containing only a low concentration of a high affinity ethylene glycol-bis(β-aminoethylether) N,N,N′,N′-tetraacetic acid (EGTA) like chelator (50–200 μM), inward membrane currents (at −50 mV) due to evoked Ca2+ release, spontaneous Ca2+ release or Ca2+ overload following long-lasting depolarizations to very positive membrane potentials are prolonged if the dialysing fluid contains a high concentration of a low affinity Ca2+ chelating compound such as citrate or free adenosine 5′-triphosphate (ATP). Without such a non-saturable Ca2+ chelator in the dialysing fluid, Ca2+-release-dependent inward currents are often oscillatory and show an irregular amplitude. With a low affinity chelator in a non-saturable concentration, discrete inward currents with constant properties can be recorded. We conclude that the variability in Ca2+-release-dependent inward current seen in single cells arises from spatial inhomogeneities of intracellular Ca2+ concentration ([Ca2+]i) due to localized saturation of endogenous and exogenous high affinity Ca2+ buffers (e.g. [2]). This can be avoided experimentally by addition of a non-saturable buffer to the intracellular solution. This condition might be useful, if properties of Ca2+ release from the SR and/ or the resulting membrane current, like for example arrhythmogenic transient inward current, are to be investigated on the single cell level.
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Lipp, P., Pott, L. Effects of intracellular Ca2+ chelating compounds on inward currents caused by Ca2+ release from sarcoplasmic reticulum in guinea-pig atrial myocytes. Pflügers Arch. 419, 296–303 (1991). https://doi.org/10.1007/BF00371110
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DOI: https://doi.org/10.1007/BF00371110