The Plasma Membrane Na+/Ca2+ Exchange Inhibitor KB-R7943 Is Also a Potent Inhibitor of the Mitochondrial Ca2+ Uniporter

Br J Pharmacol. 2007 Jul;151(5):647-54. doi: 10.1038/sj.bjp.0707260. Epub 2007 Apr 30.

Abstract

Background and purpose: The thiourea derivative KB-R7943, originally developed as inhibitor of the plasma membrane Na(+)/Ca(2+) exchanger, has been shown to protect against myocardial ischemia-reperfusion injury. We have studied here its effects on mitochondrial Ca(2+) fluxes.

Experimental approach: [Ca(2+)] in cytosol, mitochondria and endoplasmic reticulum (ER), and mitochondrial membrane potential were monitored using both luminescent (targeted aequorins) and fluorescent (fura-2, tetramethylrhodamine ethyl ester) probes in HeLa cells.

Key results: KB-R7943 was also a potent inhibitor of the mitochondrial Ca(2+) uniporter (MCU). In permeabilized HeLa cells, KB-R7943 inhibited mitochondrial Ca(2+) uptake with a Ki of 5.5+/-1.3 microM (mean+/-S.D.). In intact cells, 10 microM KB-R7943 reduced by 80% the mitochondrial [Ca(2+)] peak induced by histamine. KB-R7943 did not modify the mitochondrial membrane potential and had no effect on the mitochondrial Na(+)/Ca(2+) exchanger. KB-R7943 inhibited histamine-induced ER-Ca(2+) release in intact cells, but not in cells loaded with a Ca(2+)-chelator to damp cytosolic [Ca(2+)] changes. Therefore, inhibition of ER-Ca(2+)-release by KB-R7943 was probably due to the increased feedback Ca(2+)-inhibition of inositol 1,4,5-trisphosphate receptors after MCU block. This mechanism also explains why KB-R7943 reversibly blocked histamine-induced cytosolic [Ca(2+)] oscillations in the same range of concentrations required to inhibit MCU.

Conclusions and implications: Inhibition of MCU by KB-R7943 may contribute to its cardioprotective activity by preventing mitochondrial Ca(2+)-overload during ischemia-reperfusion. In addition, the effects of KB-R7943 on Ca(2+) homeostasis provide new evidence for the role of mitochondria modulating Ca(2+)-release and regenerative Ca(2+)-oscillations. Search for permeable and selective MCU inhibitors may yield useful pharmacological tools in the future.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aequorin / biosynthesis
  • Calcium / metabolism
  • Calcium Channels / drug effects
  • Calcium Channels / metabolism*
  • Cell Membrane / drug effects
  • Cell Membrane / enzymology
  • Cells, Cultured
  • Cytosol / drug effects
  • Cytosol / metabolism
  • Fluorescent Dyes
  • Fura-2
  • HeLa Cells
  • Histamine / pharmacology
  • Homeostasis / drug effects
  • Humans
  • Inositol 1,4,5-Trisphosphate / physiology
  • Inositol 1,4,5-Trisphosphate Receptors / drug effects
  • Membrane Potentials / drug effects
  • Mitochondria / drug effects
  • Mitochondria / metabolism*
  • Sodium-Calcium Exchanger / antagonists & inhibitors*
  • Thiourea / analogs & derivatives*
  • Thiourea / pharmacology

Substances

  • 2-(2-(4-(4-nitrobenzyloxy)phenyl)ethyl)isothiourea methanesulfonate
  • Calcium Channels
  • Fluorescent Dyes
  • Inositol 1,4,5-Trisphosphate Receptors
  • Sodium-Calcium Exchanger
  • mitochondrial calcium uniporter
  • Aequorin
  • Histamine
  • Inositol 1,4,5-Trisphosphate
  • Thiourea
  • Calcium
  • Fura-2