Isoproterenol stimulates rapid extrusion of sodium from isolated smooth muscle cells
Department of Physiology
8-Bromo Cyclic Adenosine Monophosphate; Animals; Benzofurans; Bufo marinus; Carbachol; Ethers, Cyclic; Fluorescent Dyes; Forskolin; Isoproterenol; Kinetics; Microscopy, Fluorescence; Muscle, Smooth; Ouabain; Pindolol; Potassium; Sodium; Stomach; Time Factors
Life Sciences | Medicine and Health Sciences
beta-Agonists cause an inhibition of contractility and a transient stimulation of Na+/K+ pumping in smooth muscle cells of the stomach from the toad Bufo marinus. To determine if the stimulation of Na+/K+ pumping causes changes in intracellular [Na+] ([Na+]i) that might link Na+ pump stimulation to decrease Ca2+ availability for contraction, [Na+]i was measured in these cells with SBFI, a Na(+)-sensitive fluorescent indicator. Basal [Na+]i was 12.8 +/- 4.2 mM (n = 32) and was uniform throughout the cell. In response to isoproterenol, [Na+]i decreased an average of 7.1 +/- 1.1 mM in 3 sec. Since this decrease in [Na+]i could be completely blocked by inhibition of the Na+ pump, or by blockade of the beta-receptor, [Na+]i reduction is the result of occupation of the beta-receptor by isoproterenol and subsequent stimulation of the Na+ pump. 8-Bromoadenosine 3',5'-cyclic monophosphate and forskolin mimicked the effect of isoproterenol, indicating that the sequence of events linking beta-receptor occupation to Na+ pump stimulation most likely includes activation of adenylate cyclase, production of cAMP, and stimulation of cAMP-dependent protein kinase. The decrease in [Na+]i is sufficiently large and fast that it is expected to stimulate turnover of the Na+/Ca2+ exchanger in the Ca2+ extrusion mode, thereby accounting for the observed linkage between stimulation of the Na+/K+ pump and inhibition of contractility in response to beta-adrenergic agonists.
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Citation: Proc Natl Acad Sci U S A. 1993 Sep 1;90(17):8058-62.
Proceedings of the National Academy of Sciences of the United States of America
Moore, Edwin D. W. and Fay, Fredric S., "Isoproterenol stimulates rapid extrusion of sodium from isolated smooth muscle cells" (1993). Open Access Articles. 1813.