beta-Adrenergic agonists stimulate Mg2+ uptake in mouse distal convoluted tubule cells
Monday, September 14th, 2009Kang HS, Kerstan D, Dai LJ, Ritchie G, and Quamme GA: beta-Adrenergic agonists stimulate Mg2+ uptake in mouse distal convoluted tubule cells. American Journal of Physiology 279:F1116-F1123, 2000.
Download paper
Abstract b-Adrenergic agonists influence electrolyte reabsorption in the proximal tubule, loop of Henle, and distal tubule. Although isoproterenol enhances magnesium absorption in the thick ascending limb, it is unclear what effect, if any, b-adrenergic agonists have on tubular magnesium handling. The effects of isoproterenol were studied in immortalized mouse distal convoluted tubule (MDCT) cells by measuring cellular cAMP formation with radioimmunoassays and Mg21 uptake with fluorescence techniques. Intracellular free Mg21 concentration ([Mg21]i) was measured in single MDCT cells by using microfluorescence with mag-fura-2. To assess Mg21 uptake, MDCT cells were first Mg21 depleted to 0.22 6 0.01 mM by culturing in Mg21-free media for 16 h and then placed in 1.5 mM MgCl2, and the changes in [Mg21]i were determined. [Mg21]i returned to basal levels, 0.53 6 0.02 mM, with a mean refill rate, d([Mg21]i)/dt, of 168 6 11 nM/s. Isoproterenol stimulated Mg21 entry in a concentration-dependent manner, with a maximal response of 252 6 11 nM/s, at a concentration of 1027 M, that represented a 50 6 7% increase in uptake rate above control values. This was associated with a sixfold increase in intracellular cAMP generation. Isoproterenol-stimulated Mg21 uptake was completely inhibited with RpcAMPS, a protein kinase A inhibitor, and U-73122, a phospholipase C inhibitor, and partially blocked by RO 31– 822, a protein kinase C inhibitor. Accordingly, isoproterenolmediated Mg21 entry rates involve multiple intracellular signaling pathways. Aldosterone potentiated isoproterenolstimulated Mg21 uptake (326 6 31 nM/s), whereas elevation of extracellular Ca21 inhibited isoproterenol-mediated cAMP accumulation and Mg21 uptake, 117 6 37 nM/s. These studies demonstrate that isoproterenol stimulates Mg21 uptake in a cell line of mouse distal convoluted tubules that is modulated by hormonal and extracellular influences.