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This Article Full Text Full Text (PDF) All Versions of this Article: 554/2/387    most recent jphysiol.2003.050930v1 Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by DiPolo, R. Articles by Beaugé, L. Search for Related Content PubMed PubMed Citation Articles by DiPolo, R. Articles by Beaugé, L.

¹ Laboratorio de Permeabilidad Iónica, Centro de Biofísica y Bioquímica, IVIC, Apartado 21827, Caracas 1020A, Venezuela² Laboratorio de Biofísica, Instituto de Investigación Médica M. y M. Ferreyra, INIMEC-CONICET, 5000 Córdoba, Argentina, and Marine Biological Laboratory, Woods Hole, MA 02543, USA

In squid nerves the Na⁺–Ca²⁺ exchanger is up-regulated by ATP and phosphoarginine (PA). ATP regulation involves drastic alterations in the Na⁺_i, H⁺_i and Ca²⁺_i interactions with the large intracellular cytoplasmic loop of the exchanger protein. In this work we explored the mechanisms associated with PA regulation in intracellular dialysed squid axons and squid optic nerve membrane vesicles. Dialysed axons were used to measure the four modes of exchange fluxes (Na⁺_o–Ca²⁺_i or forward exchange, Ca²⁺_o–Na⁺_i or reverse exchange, Ca²⁺_o–Ca²⁺_i exchange and Na⁺_o–Na⁺_i exchange) under controlled intra- and extracellular conditions. Inside-out membrane vesicles allowed measurement of the Na⁺-gradient-dependent ⁴⁵Ca²⁺ uptake (forward mode) as influenced by ligands and digestion with chymotrypsin from the intracellular side. The results show that, unlike ATP, PA regulation does not affect the H⁺_i, Na⁺_i and Ca²⁺_i interactions with the intracellular ‘regulatory’ loop, but increases the affinity of the intracellular transport sites, preferentially for Ca²⁺_i (about 20-fold) over Na⁺_i (50%); i.e. PA favours the forward mode over the other exchange modes. Intracellular chymotrypsin digestion removed ATP regulation while leaving modulation by PA unmodified. Western blot analysis suggested that chymotrypsin disrupts the large intracellular loop. Together these results indicate that ATP and PA regulations are associated with different structures inside and outside the exchanger protein. Based on these observations we expanded our previous model for metabolic regulation of the Na⁺–Ca²⁺ exchanger by adding to the original ‘ATP region’ a new zone, the ‘PA region’, related to the intracellular transport sites for Na⁺_i and Ca²⁺_i. This new model is able to explain most previous and present results.

(Received 8 July 2003; accepted after revision 20 October 2003; first published online 24 October 2003)
Corresponding author L. Beaugé, Laboratorio de Biofisica, Instituto de Investigación Médica M. y M. Ferreyra, Casilla de Correo 389, 5000 Córdoba, Argentina.  Email: lbeauge{at}immf.uncor.edu

This article has been cited by other articles:

				L. Beauge and R. DiPolo Dual effect of Nai+ on Ca2+ influx through the Na+/Ca2+ exchanger in dialyzed squid axons. Experimental data confirming the validity of the squid axon kinetic model Am J Physiol Cell Physiol, January 1, 2008; 294(1): C118 - C125. [Abstract] [Full Text] [PDF]

				R. Dipolo and L. Beauge Sodium/Calcium Exchanger: Influence of Metabolic Regulation on Ion Carrier Interactions Physiol Rev, January 1, 2006; 86(1): 155 - 203. [Abstract] [Full Text] [PDF]