Regulation by extracellular Na+ of cytosolic Mg2+ concentration in Mg2+‐loaded rat sublingual acini

[摘要]

The regulation of cytosolic free Mg²⁺ concentration ([Mg²⁺]_i) in Mg²⁺-loaded rat sublingual mucous acini was examined using the Mg²⁺-sensitive fluorescent indicator mag-fura-2. Loading sublingual acini with 5 mM Mg²⁺ elevated the [Mg²⁺]_i from 0.35 ± 0.01 mM to 0.66 ± 0.01 mM. Removal of extracellular Mg²⁺ resulted in a significantly faster [Mg²⁺]_i decrease in Mg²⁺-loaded rcini than in unloaded acini. Membrane depolarization with high extracellular [K⁺] and inhibition of P-type ATPases by vanadate did not alter the [Mg²⁺]_i decrease, indicating that the Mg²⁺ efflux mechanism is not electrogenic. Na⁺-free medium inhibited 80% of the [Mg²⁺]_i decrease suggesting that a Na⁺-dependent Mg²⁺ efflux pathway mediates the [Mg²⁺]_i decrease. Accordingly, the Na⁺-dependent antiport inhibitor quinidine reduced > 80% of the [Mg²⁺]_i decrease, suggesting that the Na⁺-dependent Mg⁺ efflux was also partly driven by K⁺. The [Mg⁺]_i system. Mg²⁺ efflux was also partly driven by K⁺. The [Mg²⁺]_i decrease was significantly inhibited by carbachol, a muscarinic agonist, but not by cAMP. These results indicate that in sublingual acinar cells a Na⁺-dependent pathway mediates Mg²⁺ efflux and that muscarinic stimulation may regulate Mg²⁺ extrusion.

[学科分类] 生物化学/生物物理

[关键词] Salivary acini;Mg2+ loading;[Mg2+]i decrease;Na+/Mg2+ antiport;BAPTA;bis(O-aminophenoxy)ethane-N;N;N′;N′-tetraacetic acid;BSA;bovine serum albumin;[Ca2+]i;cytosolic free Ca2+ concentration;db-cAMP;6;2′-O-dibutyladenosine 3′;5′-cyclic monophosphate;Hepes;4-(2-hydroxyethyl)-1-piperazine ethanesulphonic acid;[Mg2+]i;cytosolic free Mg2+ concentration;NMDG;N-methyl-d-glucamine;PSS;physiological salt solution