Steady-state and dynamic properties of cardiac sodium-calcium exchange. Sodium-dependent inactivation.

Abstract

A B ST RAC TSodium-calcium exchange current was isolated in inside-out patches excised from guinea pig ventricular cells using the giant patch method. The outward exchange current decayed exponentially upon activation by cytoplasmic sodium (sodium-dependent inactivation). The kinetics and mechanism of the inactivation were studied. (a) The rate of inactivation and the peak current amplitude were both strongly temperature dependent (Ql0 = 2.2). (b) An increase in cytoplasmic pH from 6.8 to 7.8 attenuated the current decay and shifted the apparent dissociation constant (/Ca) of cytoplasmic calcium for secondary activation of the exchange current from 9.6 IxM to < 0.3 ~M. (c) The amplitude of exchange current decreased synchronously over the membrane potential range from -120 to 60 mV during the inactivation, indicating that voltage dependence of the exchanger did not change during the inactivation process. The voltage dependence of exchange current also did not change during secondary modulation by cytoplasmic calcium and activation by chymotrypsin. (el) In the presence of 150 mM extracellular sodium and 2 mM extracellular calcium, outward exchange current decayed similarly upon application of cytoplasmic sodium. Upon removal of cytoplasmic sodium in the presence of 2-5 JiM cytoplasmic free calcium, the inward exchange current developed in two phases, a fast phase within the time course of solution changes, and a slow phase (~ = 4 s) indicative of recovery from sodium-dependent inactivation. (e) Under zero-trans conditions, the inward current was fully activated within solution switch times upon application of cytoplasmic calcium and did not decay. (f) The slow recovery phase of inward current upon removal of cytoplasmic sodium was also present under the zero-trans condition. (g) Sodium-dependent inactivation shows little or no dependence on membrane potential in guinea pig myocyte sarcolemma. (h) Sodium-dependent inactivation of outward current is attenuated in rate and extent as extracellular calcium is decreased.

Role of Na+/Ca2+exchanger in Ca2+homeostasis in rat suprachiasmatic nucleus neurons

“…In contrast, in the presence of 1 M monensin to raise [Na ϩ ] i , 0 Na ϩ rapidly increased [Ca 2ϩ ] i . The 0 Na ϩ -induced increase of [Ca 2ϩ ] i inactivated during the 4-min period of Na ϩ removal, likely mediated by Na ϩ -dependent inactivation of reverse NCX (Hilgemann et al 1992b).…”

K+-Dependent Na+/Ca2+Exchangers: Key Contributors to Ca2+Signaling

“…NCKX2 and 4 were found to be alternatively spliced, with the longer forms possessing an additional 17 or 19 amino acid residues, respectively, in the large cytosolic loops, although there are no obvious functional consequences and no detailed analyses of possible differential regulation have been performed (36,47,59). However, NCKX2 was recently shown to become inactivated in a time-and Na + -dependent manner, a phenomenon that has already been well described for NCX1 (16), suggesting that NCKX2 is also subject to ionic regulation (1). Physiologically, high internal Na + levels that result from persistent neuronal membrane depolarization may inactivate NCKX2, leading to persistent Ca 2+ elevation.…”

PKC-Independent Stimulation of Cardiac Na+/Ca2+ Exchanger by Staurosporine

“…Third, the removal of Na + -inactivation by STS should be addressed. It has been known that, intracellular Na + -induced inactivation of outward NCX1 current is ablated by allosteric Ca 2+ activation (Hilgemann et al, 1992b;Reeves and Condrescu, 2003). If STS interferes with the process of Na + -inactivation, it can ablate the inactivation and enhance the reverse exchanger, as intracellular Ca 2+ does.…”

“…The forward mode of NCX1 produces an inward exchange current and removes Ca 2+ out of the cells, while the reverse mode generates an outward exchange current and brings Ca 2+ into the cells. Regulations of NCX1 by cytoplasmic Ca 2+ and membrane phosphatidylionositol-4,5-bis-phosphate (PIP2) have been well described in excised giant patch membranes (Hilgemann, 1990;Hilgemann et al, 1992a;Hilgemann et al, 1992b;Hilgemann and Ball, 1996). The action of PIP2 on NCX1 can be determined by phospholipase C (PLC) activity.…”

“…The action of PIP2 on NCX1 can be determined by phospholipase C (PLC) activity. The effects of cytoplasmic Ca 2+ on NCX1 can be mediated by either direct allosteric Ca 2+ activation (Hilgemann et al, 1992b;Reeves and Condrescu, 2003) or multiple Ca 2+ dependent signaling pathways (Iwamoto et al, 1998;Opuni and Reeves, 2000;Katanosaka et al, 2005;Zhang et al, 2006;Yaradanakul et al, 2007).…”