Properties of Na⁺-independent passive Mg²⁺ influx in pig carotid artery

Abstract

Two pathways have been proposed for Mg²⁺ transport across the plasma membrane: 1) Na⁺-Mg²⁺ exchange and 2) Na⁺-independent passive Mg²⁺ pathway in visceral smooth muscle (Nakayama et al. J. Physiol.551.3,843-853,2003). Recently, Nadler et al. (Nature411,590-595,2001) has identified LTRPC7 as a Mg²⁺ permeable channel in the plasma membrane. In this study, using 31P-nuclear magnetic resonance (NMR), we measured the intracellular free-Mg²⁺ concentration ([Mg²⁺]_i) in pig carotid artery smooth muscle. [Mg²⁺]_i was estimated from the chemical shift of the β-ATP peak. Intracellular pH (pH_i) estimated from the chemical shift of P_i was used to correct the [Mg²⁺]_i value. We found that [Mg²⁺]_i was increased by increasing the extracellular Mg²⁺ concentration in the absence of Ca²⁺. This was true when extracellular Na⁺ was substituted with equimolar K⁺ or NMDG(N-methyl-D-glucamine). 2-APB is a known potent blocker for LTRPC7. We also examined whether this drug affects the Na⁺-independent [Mg²⁺]_i rise. [Jpn J Physiol 54 Suppl:S122 (2004)]