Quantitative analysis of the Ca2+-dependent regulation of delayed rectifier K+ current IKs in rabbit ventricular myocytes

Daniel C. Bartos, Stefano Morotti, Kenneth S Ginsburg, Eleonora Grandi, Donald M Bers

Research output: Contribution to journalArticle

16 Scopus citations

Abstract

Key points: [Ca2+]i enhanced rabbit ventricular slowly activating delayed rectifier K+ current (IKs) by negatively shifting the voltage dependence of activation and slowing deactivation, similar to perfusion of isoproterenol. Rabbit ventricular rapidly activating delayed rectifier K+ current (IKr) amplitude and voltage dependence were unaffected by high [Ca2+]i. When measuring or simulating IKs during an action potential, IKs was not different during a physiological Ca2+ transient or when [Ca2+]i was buffered to 500 nm. Abstract: The slowly activating delayed rectifier K+ current (IKs) contributes to repolarization of the cardiac action potential (AP). Intracellular Ca2+ ([Ca2+]i) and β-adrenergic receptor (β-AR) stimulation modulate IKs amplitude and kinetics, but details of these important IKs regulators and their interaction are limited. We assessed the [Ca2+]i dependence of IKs in steady-state conditions and with dynamically changing membrane potential and [Ca2+]i during an AP. IKs was recorded from freshly isolated rabbit ventricular myocytes using whole-cell patch clamp. With intracellular pipette solutions that controlled free [Ca2+]i, we found that raising [Ca2+]i from 100 to 600 nm produced similar increases in IKs as did β-AR activation, and the effects appeared additive. Both β-AR activation and high [Ca2+]i increased maximally activated tail IKs, negatively shifted the voltage dependence of activation, and slowed deactivation kinetics. These data informed changes in our well-established mathematical model of the rabbit myocyte. In both AP-clamp experiments and simulations, IKs recorded during a normal physiological Ca2+ transient was similar to IKs measured with [Ca2+]i clamped at 500–600 nm. Thus, our study provides novel quantitative data as to how physiological [Ca2+]i regulates IKs amplitude and kinetics during the normal rabbit AP. Our results suggest that micromolar [Ca2+]i, in the submembrane or junctional cleft space, is not required to maximize [Ca2+]i-dependent IKs activation during normal Ca2+ transients. (Figure presented.).

Original languageEnglish (US)
Pages (from-to)2253-2268
Number of pages16
JournalJournal of Physiology
Volume595
Issue number7
DOIs
StatePublished - Apr 1 2017

Keywords

  • action potential
  • cardiac electrophysiology
  • delayed rectifier current
  • intracellular calcium
  • potassium channel
  • rabbit
  • voltage-gated channels

ASJC Scopus subject areas

  • Physiology

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