Microdomain [Ca²⁺] near ryanodine receptors as reported by L-type Ca²⁺ and Na+/Ca²⁺ exchange currents

J Physiol. 2011 May 15;589(Pt 10):2569-83. doi: 10.1113/jphysiol.2010.202663. Epub 2011 Mar 8.

Abstract

During Ca²⁺ release from the sarcoplasmic reticulum triggered by Ca²⁺ influx through L-type Ca²⁺ channels (LTCCs), [Ca²⁺] near release sites ([Ca²⁺]nrs) temporarily exceeds global cytosolic [Ca²⁺]. [Ca²⁺]nrs can at present not be measured directly but the Na+/Ca2+ exchanger (NCX) near release sites and LTCCs also experience [Ca²⁺]nrs. We have tested the hypothesis that ICaL and INCX could be calibrated to report [Ca²⁺]nrs and would report different time course and values for local [Ca²⁺]. Experiments were performed in pig ventricular myocytes (whole-cell voltage-clamp, Fluo-3 to monitor global cytosolic [Ca²⁺], 37◦C). [Ca²⁺]nrs-dependent inactivation of ICaL during a step to +10 mV peaked around 10 ms. For INCX we computationally isolateda current fraction activated by [Ca²⁺]nrs; values were maximal at 10 ms into depolarization. The recovery of [Ca²⁺]nrs was comparable with both reporters (>90% within 50 ms). Calibration yielded maximal values for [Ca²⁺]nrs between 10 and 15 μmol l⁻¹ with both methods. When applied to a step to less positive potentials (-30 to -20 mV), the time course of [Ca²⁺]nrs was slower but peak values were not very different. In conclusion, both ICaL inactivation and INCX activation, using a subcomponent analysis, can be used to report dynamic changes of [Ca²⁺]nrs. Absolute values obtained by these different methods are within the same range, suggesting that they are reporting on a similar functional compartment near ryanodine receptors. Comparable [Ca²⁺]nrs at +10 mV and -20 mV suggests that, although the number of activated release sites differs at these potentials, local gradients at release sites can reach similar values.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Aniline Compounds / administration & dosage
  • Animals
  • Calcium / analysis
  • Calcium / metabolism
  • Calcium / physiology
  • Calcium Channels, L-Type / physiology
  • Fluorescent Dyes / administration & dosage
  • Membrane Microdomains / physiology*
  • Membrane Potentials / physiology
  • Myocytes, Cardiac / physiology
  • Ryanodine Receptor Calcium Release Channel / physiology*
  • Sarcoplasmic Reticulum / metabolism
  • Sarcoplasmic Reticulum / physiology
  • Sodium-Calcium Exchanger / physiology*
  • Swine
  • Ventricular Function
  • Xanthenes / administration & dosage

Substances

  • Aniline Compounds
  • Calcium Channels, L-Type
  • Fluorescent Dyes
  • Ryanodine Receptor Calcium Release Channel
  • Sodium-Calcium Exchanger
  • Xanthenes
  • Fluo-3
  • Calcium