Na+/Ca2+ countertransport in plasma membrane of rat pancreatic acinar cells

Bayerdörffer, Eckehard; Haase, Winfried; Schulz, Irene

doi:10.1007/bf01870657

Cited by 25 publications

(8 citation statements)

References 44 publications

(83 reference statements)

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“…The low capacity cannot be explained by artifacts introduced by the isolation procedure. A 2.5% recovery and a 9.3-fold purification of the plasma membrane marker Na+/K +-ATPase are congruent with data previously published by us [26,37] and by others [3,16,19] on a variety of Ca 2 § transporting epithelia. One could argue that a loss of calmodulin during the isolation procedure resulted in the low V~ observed.…”

Section: Atp-energized Ca 2+ Transportsupporting

confidence: 91%

Calcium absorption by fish intestine: The involvement of ATP-and sodium-dependent calcium extrusion mechanisms

et al. 1990

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Measurements of unidirectional calcium fluxes in stripped intestinal epithelium of the tilapia, Oreochromis mossambicus, in the presence of ouabain or in the absence of sodium indicated that calcium absorption via the fish intestine is sodium dependent. Active Ca2+ transport mechanisms in the enterocyte plasma membrane were analyzed. The maximum capacity of the ATP-dependent Ca2+ pump (Vm: 0.63 nmol.min-1.mg-1, Km:27 nM Ca2+) is calculated to be 2.17 nmol.min-1.mg-1, correcting for 29% inside-out oriented vesicles in the membrane preparation. The maximum capacity of the Na+/Ca2+ exchanger with high affinity for Ca2+ (Vm:7.2 nmol.min-1.mg-1, Km:181 nM Ca2+) is calculated to be 13.6 nmol.min-1.mg-1, correcting for 53% resealed vesicles and assuming symmetrical behavior of the Na+/Ca2+ exchanger. The high affinity for Ca2+ and the sixfold higher capacity of the exchanger compared to the ATPase suggest strongly that the Na+/Ca2+ exchanger will contribute substantially to Ca2+ extrusion in the fish enterocyte. Further evidence for an important contribution of Na+/Ca2+ exchange to Ca2+ extrusion was obtained from studies in which the simultaneous operation of ATP- and Na(+)-gradient-driven Ca2+ pumps in inside-out vesicles was evaluated. The fish enterocyte appears to present a model for a Ca2+ transporting cell, in which Na+/Ca2+ exchange activity with high affinity for Ca2+ extrudes Ca2+ from the cell.

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Section: Atp-energized Ca 2+ Transportsupporting

confidence: 91%

Calcium absorption by fish intestine: The involvement of ATP-and sodium-dependent calcium extrusion mechanisms

et al. 1990

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“…In the rat pancreas, we have found that NCLX is primarily found in the exocrine part (data not shown). In this regard, Na ϩ /Ca 2ϩ exchange in pancreatic ducts was reported previously to be more intense than in acini where the plasma membrane Ca 2ϩ pump is the primary transporter for Ca 2ϩ efflux (26). In mouse brain, NCX2 was recently shown to play a role in synaptic transmission, and specifically, in the context of learning and memory (27).…”

Section: Figmentioning

confidence: 99%

Lithium-Calcium Exchange Is Mediated by a Distinct Potassium-independent Sodium-Calcium Exchanger

Palty

Ohana

Hershfinkel

et al. 2004

Journal of Biological Chemistry

130

123

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Sodium-calcium exchangers have long been considered inert with respect to monovalent cations such as lithium, choline, and N-methyl-D-glucamine. A key question that has remained unsolved is how despite this, Li ؉ catalyzes calcium exchange in mammalian tissues. Here we report that a Na ؉ /Ca 2؉ exchanger, NCLX cloned from human cells (known as FLJ22233), is distinct from both known forms of the exchanger, NCX and NCKX in structure and kinetics. Surprisingly, NCLX catalyzes active Li ؉ /Ca 2؉ exchange, thereby explaining the exchange of these ions in mammalian tissues. The NCLX protein, detected as both 70-and 55-KDa polypeptides, is highly expressed in rat pancreas, skeletal muscle, and stomach. We demonstrate, moreover, that NCLX is a K ؉ -independent exchanger that catalyzes Ca 2؉ flux at a rate comparable with NCX1 but without promoting Na ؉ /Ba 2؉ exchange. The activity of NCLX is strongly inhibited by zinc, although it does not transport this cation. NCLX activity is only partially inhibited by the NCX inhibitor, KB-R7943. Our results provide a cogent explanation for a fundamental question. How can Li ؉ promote Ca 2؉ exchange whereas the known exchangers are inert to Li ؉ ions? Identification of this novel member of the Na ؉ / Ca 2؉ superfamily, with distinct characteristics, including the ability to transport Li ؉ , may provide an explanation for this phenomenon.Plasma membrane Na ϩ /Ca 2ϩ exchange is an important element in cellular Ca 2ϩ homeostasis. It has been extensively investigated in mammals, especially in cardiac and neuronal tissues (1), where this mechanism is essential for regulation of Ca 2ϩ homeostasis. Na ϩ /Ca 2ϩ exchange also plays a key role in many other organs and tissues by modulating the intracellular Ca 2ϩ response (2). The Na ϩ /Ca 2ϩ exchangers described to date are members of four major families (1). Of these, only NCX1-3 and NCKX1-4 are found in mammalian cells, whereas the other two are expressed in plants, yeast, and bacteria.The stoichiometry of NCX exchangers is based on 3-4Na ϩ / 1Ca 2ϩ , and the protein is structurally organized as nine transmembrane helixes divided by a large cytoplasmic loop (3). NCKX family proteins have a stoichiometry of 4Na/1Ca/1K, and their topology is thought to consist of two sets of five membrane helixes divided by a cytoplasmic loop and NH 2 -terminal extracellular domain (4). The two families share several important functional and structural motifs: a structural hallmark of the Na ϩ /Ca 2ϩ exchanger superfamily is the presence of two regions of sequence similarity, called ␣1 and ␣2, which are considered necessary and sufficient for generating exchange activity (1, 5). Functionally, these exchangers are considered catalytically inert to inorganic and organic monovalent cations such as Li ϩ , NMG ϩ , 1 and choline ϩ , which are often used in "sodium-free" solutions to reverse Na ϩ /Ca 2ϩ exchange activity (2).Although Li ϩ ions are not transported by either NCX or NCKX, numerous physiological studies have reported a significant effect of this ion ...

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“…Under these conditions calcium entry into the acinar cell triggered by endoplasmic reticulum store depletion continues unabated [11,30,48] . This is of particular significance since the Na + /Ca 2+ exchanger is not present in the pancreatic acinar cell and cannot contribute to the control of these calcium changes [11,84,85] . The importance of intracellular ATP levels in cytosolic calcium clearance has been highlighted in experiments where supplementary ATP was administered directly into the acinar cell interior via patch pipette [36] .…”

Section: Mitochondrial Dysfunctionmentioning

confidence: 99%