NDLI: Characterization of the relationship between Na+–Ca2+ exchange rate and cytosolic calcium in trout cardiac myocytes

Content Provider	Springer Nature Link
Author	Hove Madsen, Leif Tort, Lluis
Copyright Year	2000
Abstract	The whole-cell patch-clamp technique combined with rapid caffeine (CAF) applications was used to measure Na+–Ca2+ exchange (NCX) currents (I NCX). The rate of Ca2+ extrusion and the amount of Ca2+ extruded from the cell upon a rapid CAF exposure were obtained from I NCX and its time integral, respectively. This gave a maximal NCX rate ( $\dot V_{{\rm NCX}} $ ) of 151 amol pF–1 s–1 or 2.3 mM s–1 and a half-maximal $\dot V_{{\rm NCX}} $ (K 0.5) at a total cellular [Ca2+] ([Ca2+]tot) of 15.4 amol pF–1. Using the same approach for the tail current induced by repolarization to –80 mV gave a K 0.5 of 7.0 amol pF–1 corresponding to 108 µM total or 2–4 µM free Ca2+. The relationship between [Ca2+]tot and $\dot V_{{\rm NCX}} $ was linear in the physiological range. Inhibition of the SR function with cyclopiazonic acid plus ryanodine reduced the slope significantly from 23.2±1.4 to 17.6±1.6 s–1, while ryanodine alone had no effect. The relationship between [Ca2+]tot and $\dot V_{{\rm NCX}} $ was steeper at more negative membrane potentials, and with identical SR Ca2+ loads the maximal $\dot V_{{\rm NCX}} $ at –10 mV was reduced to 39.7±2.7% of the value at –90 mV. Long depolarizations caused SR Ca2+ loading through reverse-mode NCX. Between –30 and +10 mV reverse mode $\dot V_{{\rm NCX}} $ =V m·0.047 amol pF–1 s–1 mV–1+2.51 amol pF–1 s–1, giving a reversal potential of –54 mV. In conclusion, the relationship between $\dot V_{{\rm NCX}} $ and [Ca2+]tot shows that the NCX is capable of removing a total Ca2+ transient of 60 µM at physiological heart rates, while reverse-mode NCX reloads the sarcoplasmic reticulum (SR) during depolarization. Furthermore, small alterations in the action potential configuration are predicted to change significantly the relative importance of the NCX in the regulation of cytosolic [Ca2+] and SR Ca2+ loading.
Starting Page	701
Ending Page	708
Page Count	8
File Format	PDF
ISSN	00316768
Journal	Pflügers Archiv
Volume Number	441
Issue Number	5
e-ISSN	14322013
Language	English
Publisher	Springer-Verlag
Publisher Date	2000-12-15
Publisher Place	Berlin, Heidelberg
Access Restriction	One Nation One Subscription (ONOS)
Subject Keyword	Human Physiology
Content Type	Text
Resource Type	Article
Subject	Physiology Physiology (medical) Clinical Biochemistry

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