J Mol Cell Cardiol 34, 197–207 (2002) doi:10.1006/jmcc.2001.1502, available online at http://www.idealibrary.com on Effects of Components of Ischemia on the Kv4.3 Current Stably Expressed in Chinese Hamster Ovary Cells Suresh Singarayar 1 , Cameron Singleton 1 , Hui Tie 1 , Ken Wyse 1 , Jane Bursill 1 , Asne Bauskin 2 , Wan Wu 2 , Stella Valenzuela 2 , Samuel Breit 2 and Terence Campbell 1 1 Department of Medicine, The University of New South Wales and the Victor Chang Cardiac Research Institute, Sydney Australia and 2 Centre for Immunology, St Vincent’s Hospital, Sydney, Australia (Received 15 May 2001, accepted for publication 9 November 2001) S. S, C. S, H. T, K. W, J. B, A. B, W. W, S. V, S. B  T. C. Effects of Components of Ischemia on the Kv4.3 Current Stably Expressed in Chinese Hamster Ovary Cells. Journal of Molecular and Cellular Cardiology (2002) 34, 197–207. We investigated the effects of three components of ischemia: external acidosis (pH=6.0), extracellular hyperkalemia ([K + ]=20 mmol/l), and resting membrane depolarization to -60mV, on Kv4.3 current stably expressed in Chinese Hamster Ovary cells. We used single electrode whole cell patch clamp techniques to study changes in the current elicited. External acidosis caused a positive shift in the steady state activation curve from -13.4±2.1 mV to -3.3±1.5 mV (n=8, P= 0.004) and the steady state inactivation curve from -56.5±0.4 mV to -46.7±0.5 mV (n=14, P<0.0001). Acidosis also caused an acceleration of recovery from inactivation with the t 1/2 decreasing from 306 ms (95% CI 287–327 ms) to 194 ms (95% CI 182–207 ms), (n=14, P<0.05). Hyperkalemia did not affect any of these parameters. Combined acidosis and hyperkalemia produced effects similar to those seen with acidosis. Changing the holding potential from -90 mV to -60 mV with test potentials of +5 and +85 mV decreased the peak currents by 34.1% and 32.4% respectively (n=14). However, in the presence of external acidosis the decrease in peak currents induced by changing the holding potential was less marked. In acidotic bath the peak current at -60 mV was reduced by only 13.6% at a test potential of +5 mV and 12.3% at a test potential of +85 mV (n=14). Taken together our data suggest that the membrane depolarization and changes in pH which occur under ischemic conditions would be accompanied by relative preservation of Kv4.3 currents and provide a molecular basis for the observation of preserved epicardial I to and epicardial action potential duration (APD) shortening in ischemia.  2002 Elsevier Science Ltd. K W: Kv4.3; Transient outward current; Ischemia; Acidosis; Hyperkalemia. voltage plateau (phase 2) of the action potential, it Introduction affects the activity of other voltage-gated currents active during phases 2 and 3. Two components of The transient outward current (I to ) is responsible for the early phase of repolarization of the cardiac this current have been identified: I to1 is a voltage- activated potassium current which is calcium-in- myocyte, referred to as phase 1 or the “notch” of the cardiac action potential. This current rapidly dependent and sensitive to inhibition by 4-amino- pyridine; I to2 is a smaller calcium-activated current inactivates and therefore there is little I to during the terminal phase of repolarization (phase 3). However, carried by chloride ions. 1 An increased density of I to in the epicardium in since I to contributes to setting the height of the Please address all correspondence to: Professor T. J. Campbell, Department of Medicine, St Vincent’s Hospital, Victoria Street, Darlinghurst, Sydney, NSW, 2010, Australia. Tel: +61 2 8382 2352. Fax: +61 2 8382 2201. E-mail: T.Campbell@unsw.edu.au 0022–2828/02/020197+11 $35.00/0  2002 Elsevier Science Ltd.