This Article Full Text Full Text (PDF) All Versions of this Article: biophysj.106.082495v1 91/1/244    most recent Alert me when this article is cited Alert me if a correction is posted Services 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 Google Scholar Google Scholar Articles by Tashiro, M. Articles by Konishi, M. Search for Related Content PubMed PubMed Citation Articles by Tashiro, M. Articles by Konishi, M.

Effects of Intracellular and Extracellular Concentrations of Ca²⁺, K⁺, and Cl^– on the Na⁺-Dependent Mg²⁺ Efflux in Rat Ventricular Myocytes

Department of Physiology, Tokyo Medical University, Tokyo, Japan

Correspondence: Address reprint requests to Dr. Masato Konishi, Dept. of Physiology, Tokyo Medical University, 6-1-1 Shinjuku, Shinjuku-ku, Tokyo 160-8402, Japan. Tel.: 81-3-3351-6141; Fax: 81-3-5379-0658; E-mail: mkonishi{at}tokyo-med.ac.jp.

Intracellular Mg²⁺ concentration ([Mg²⁺]_i) was measured in rat ventricular myocytes with the fluorescent indicator furaptra (25°C). After the myocytes were loaded with Mg²⁺, the initial rate of decrease in [Mg²⁺]_i (initial [Mg²⁺]_i/t) was estimated upon introduction of extracellular Na⁺, as an index of the rate of Na⁺-dependent Mg²⁺ efflux. The initial [Mg²⁺]_i/t values with 140 mM [Na⁺]_o were essentially unchanged by the addition of extracellular Ca²⁺ up to 1 mM (107.3 ± 8.7% of the control value measured at 0 mM [Ca²⁺]_o in the presence of 0.1 mM EGTA, n = 5). Intracellular loading of a Ca²⁺ chelator, either BAPTA or dimethyl BAPTA, by incubation with its acetoxymethyl ester form (5 µM for 3.5 h) did not significantly change the initial [Mg²⁺]_i/t: 115.2 ± 7.5% (seven BAPTA-loaded cells) and 109.5 ± 10.9% (four dimethyl BAPTA loaded cells) of the control values measured in the absence of an intracellular chelator. Extracellular and/or intracellular concentrations of K⁺ and Cl^– were modified under constant [Na⁺]_o (70 mM), [Ca²⁺]_o (0 mM with 0.1 mM EGTA), and membrane potential (–13 mV with the amphotericin-B-perforated patch-clamp technique). None of the following conditions significantly changed the initial [Mg²⁺]_i/t: 1), changes in [K⁺]_o between 0 mM and 75 mM (65.6 ± 5.0% (n = 11) and 79.0 ± 6.0% (n = 8), respectively, of the control values measured at 140 mM [Na⁺]_o without any modification of extracellular and intracellular K⁺ and Cl^–); 2), intracellular perfusion with K⁺-free (Cs⁺-substituted) solution from the patch pipette in combination with removal of extracellular K⁺ (77.7 ± 8.2%, n = 8); and 3), extracellular and intracellular perfusion with K⁺-free and Cl^–-free solutions (71.6 ± 5.1%, n = 5). These results suggest that Mg²⁺ is transported in exchange with Na⁺, but not with Ca²⁺, K⁺, or Cl^–, in cardiac myocytes.