Abstract
Our understanding of the control and effects of intracellular [Na+] ([Na+]i) in intact smooth muscle is limited by the lack of data concerning [Na+]i. The initial aim of this work was therefore to investigate the suitability of using the Na+-sensitive fluorophore SBFI in intact smooth muscle. We find this to be a good method for measuring [Na+]i in ureteric smooth muscle. Resting [Na+]i was found to be around 10 mM and rose to 25 mM when the Na+-K+-ATPase was inhibited by ouabain. This relatively low [Na+]i in the absence of Na+-K+-ATPase suggests that other cellular processes, such as Na+-Ca2+ exchange, play a role in maintaining [Na+]i under these conditions. Simultaneous measurements of [Na+]i or [Ca2+] i and force showed that Na+-Ca2+ exchange can play a functional role in ureteric smooth muscle. We found that the greater the driving force for Na+ exit and hence Ca2+ entry, the larger the contraction. In addition the Na+-Ca2+ exchanger activity under these conditions was found to be pH sensitive: acidification reduced the contraction and concomitant changes in [Ca2+] and [Na+]i. We conclude that SBFI is a useful method for monitoring [Na] in smooth muscle and that Na+-Ca2+ exchange may play a functional role in the ureter.
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Received: 26 August 1997 / Received after revision: 27 October 1997 / Accepted: 28 October 1997
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Lamont, C., Burdyga, T. & Wray, S. Intracellular Na+ measurements in smooth muscle using SBFI – changes in [Na+], Ca2+ and force in normal and Na+-loaded ureter. Pflügers Arch 435, 523–527 (1998). https://doi.org/10.1007/s004240050548
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DOI: https://doi.org/10.1007/s004240050548