beta-Adrenergic agonists stimulate Mg2+ uptake in mouse distal convoluted tubule cells

greedy — Mon, 14 Sep 2009 23:57:34 +0000

Kang 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.

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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.

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.

Dr. Long Jun Dai » 2000

beta-Adrenergic agonists stimulate Mg2+ uptake in mouse distal convoluted tubule cells