caa a22 4500 477120873 CHVBK 20180405111636.0 cr unu---uuuuu 170330e19960301xx s 000 0 eng 10.1007/BF00408648 doi (NATIONALLICENCE)springer-10.1007/BF00408648 Early after-depolarisations induced by noradrenaline may be initiated by calcium released from sarcoplasmic reticulum [Elektronische Daten] [Robert Janiak, Bohdan Lewartowski] We investigated the effect of 10−8 M noradrenaline (NA) on [Ca2+], and electrical activity of single myocytes of guinea-pig ventricular myocardium loaded with Indo 1-AM. Membrane potential was recorded by means of the patch electrode and patch amplifier set to the current clamp mode. Cells were stimulated at a rate of 30/min by 3 ms pulses of the current injected through the recording electrode. Superfusion of NA resulted in slight shortening of action potentials (APs), increase in rate of rise and amplitude of the respective Ca2+ transients, and appearance of secondary Ca2+ transients of two kinds: 1. appearing before repolarisation of AP and decay of the preceding Ca2+ transient were completed and 2. appearing between the APs. We named them early after-transients (EAT) and delayed after-transients (DAT), respectively. Without any additional intervention EATS caused some prolongation of APs duration and DATs resulted in subthreshold delayed after-depolarisations (DADS). When sarcolemmal K+ conductance was decreased by tetraethylammonium (TEA) in the patch electrode or 20 μM BaCl2 in the Tyrode solution, EATs initiated early after depolarizations (EADs) and DATs initiated suprathreshold DADs triggering full-sized APs. Superfusion of 30.0 mM Na+ (replaced with LiCl) resulted in reduction of AP duration by -70% and appearance of DATs. Also, the frequent multiple oscillations of Ca 2+ concentration were often observed. Neither DATs nor the oscillations had any affect on electrical activity of the cells. Their electrogenicity could not be increased by TEA or 20.0 μM Ba2+. EATs and DATs and their respective EADs and DADs could not be initiated by NA or low Na+ superfusion in the cells pretreated with 2 × 10−7 M thapsigargin, a selective blocker of Ca2+-ATPase of sarcoplasmic reticulum (SR). We conclude that in contrast to the current hypothesis, EADs can be initiated by Ca2+ released early in the cardiac cycle from the overloaded SR, and that electrogenicity of both types of Ca2+ oscillations critically depends on the sarcolemmal K+ conductance. Kluwer Academic Publishers, 1996 cardiac myocytes nationallicence early after depolarisations nationallicence delayed after depolarisations nationallicence calcium nationallicence sarcoplasmic reticulum nationallicence noradrenaline nationallicence Janiak Robert Department of Clinical Physiology, Medical Center of Postgraduate Education, Marymoncka St. 99, 01-813, Warsaw, Poland aut Lewartowski Bohdan Department of Clinical Physiology, Medical Center of Postgraduate Education, Marymoncka St. 99, 01-813, Warsaw, Poland aut Molecular and Cellular Biochemistry Kluwer Academic Publishers; http://www.wkap.nl 163-164/1(1996-03-01), 125-130 0300-8177 163-164:1<125 1996 163-164 11010 https://doi.org/10.1007/BF00408648 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1007/BF00408648 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Janiak Robert Department of Clinical Physiology, Medical Center of Postgraduate Education, Marymoncka St. 99, 01-813, Warsaw, Poland aut NATIONALLICENCE 700 1- Lewartowski Bohdan Department of Clinical Physiology, Medical Center of Postgraduate Education, Marymoncka St. 99, 01-813, Warsaw, Poland aut NATIONALLICENCE 773 0- Molecular and Cellular Biochemistry Kluwer Academic Publishers; http://www.wkap.nl 163-164/1(1996-03-01), 125-130 0300-8177 163-164:1<125 1996 163-164 11010 Metadata rights reserved Springer special CC-BY-NC licence nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-springer