Regulation of Intracellular Calcium in Cultured Renal Epithelioid (MDCK-) Cells

The events accounting for the adaptation of the sodium-dependent phosphate cotransport (Na-Pi) to phosphate deprivation other than genomic regulation remain unknown. The involvement of changes in intracellular calcium concentration was investigated in Madin-Darby canine kidney (MDCK) cells. Calcium concentration was decreased by 15 h of phosphate deprivation (-24 to -35%) or low-calcium medium (calcium deprivation) (-45%), or 8-(N,N'-diethylamino)octyl-3,4,5-trimethoxybenzoate (TMB8) (-32%). Calcium deprivation stimulated Na-Pi (2-fold at 1 h and up to 15 h) by increasing the affinity for phosphate. Combined calcium and phosphate deprivation had more than additive effects on phosphate uptake. The effect of a 15-h calcium deprivation, but not of a 2-h one, was dependent on gene transcription and protein synthesis. TMB8 stimulated phosphate uptake similarly to phosphate deprivation (increase in maximum velocity dependent on gene transcription). The ionophore A23187 decreased basal Na-Pi as well as its stimulation by phosphate or calcium deprivation or by TMB8. Calcium deprivation stimulated (3.2-fold increase) the sodium-coupled alanine transport, whereas phosphate deprivation and TMB8 did not. We conclude that 1) phosphate deprivation decreases intracellular calcium concentration, 2) low intracellular calcium concentration is instrumental in the stimulation by prolonged calcium or phosphate deprivation of Na-Pi, and 3) phosphate or calcium deprivation modulates Na-Pi through different cellular pathways.

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A23187 increases permeability of MDCK monolayers independent of phospholipase activation

AJP Cell Physiology ◽

10.1152/ajpcell.1990.259.1.c69 ◽

1990 ◽

Vol 259 (1) ◽

pp. C69-C76 ◽

Cited By ~ 11

Author(s):

M. W. Peterson ◽

D. Gruenhaupt

Keyword(s):

Intracellular Calcium ◽

Mdck Cells ◽

Pla2 Activity ◽

Madin Darby Canine Kidney ◽

Barrier Integrity ◽

Kinase C ◽

Relationship Of ◽

The Relationship ◽

Epithelium Cells ◽

Darby Canine Kidney

Changes in intracellular calcium influence epithelial barrier integrity, but the mechanism of action is unknown. One possibility is that calcium may work by increasing phospholipase A2 (PLA2) and/or phospholipase C (PLG) activity. Measuring the mannitol permeability (Pmann) of cultured monolayers of Madin-Darby canine kidney (MDCK) epithelium cells as a measure of barrier integrity, we found that exposure of the monolayers to 5 and 10 microM A23187 produced an increase in Pmann whereas 1 microM A23187 did not. Exposure of MDCK cells labeled with [3H]arachidonate to A23187 resulted in an increase in both PLA2 activity, as measured by an increase in free fatty acids, and in PLC activity, as measured by an increase in diacylglycerol (DAG). The increase in DAG was due to an increase in phosphatidylcholine-specific PLC activity. The relationship of phospholipolysis to Pmann was evaluated further by the use of mepacrine and dexamethasone. Mepacrine (10 microM) decreased PLA2 activity by 60% but had no effect on increased Pmann after exposure to A23187. Preexposure of the monolayers to dexamethasone (10 microM) blocked both PLA2 activity and PLC activity and also prevented the increase in Pmann after exposure to A23187. To evaluate whether this protective effect of dexamethasone was due to PLC blockade, we incubated the cells with the protein kinase C blocker H-7. Incubation with H-7 offered no protection from increased Pmann after A23187. These results demonstrate that increased intracellular calcium decreases the barrier integrity of epithelium and increases both PLA2 and phosphatidylcholine-specific PLC activity. The increase in Pmann, however, appears to occur through mechanisms other than phospholipase activation.

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The lysosomal compartment as intracellular calcium store in MDCK cells: a possible involvement in InsP3-mediated Ca2+ release

Cell Calcium ◽

10.1016/s0143-4160(96)90084-6 ◽

1996 ◽

Vol 19 (2) ◽

pp. 157-165 ◽

Cited By ~ 75

Author(s):

T. Haller ◽

P. Dietl ◽

P. Deetjen ◽

H. Völkl

Keyword(s):

Intracellular Calcium ◽

Mdck Cells ◽

Calcium Store ◽

Lysosomal Compartment ◽

Intracellular Calcium Store

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Ultra-Rapid Freezing of Isolated Skeletal Muscle Fibers

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100080316 ◽

1977 ◽

Vol 35 ◽

pp. 576-577

Author(s):

Joachim R. Sommer ◽

Nancy R. Wallace

Keyword(s):

Skeletal Muscle ◽

Sarcoplasmic Reticulum ◽

Granular Material ◽

Nuclear Envelope ◽

Intracellular Calcium ◽

Ruthenium Red ◽

Threshold Concentration ◽

Rapid Freezing ◽

Frog Skeletal Muscle ◽

Electrical Isolation

After Howell (1) had shown that ruthenium red treatment of fixed frog skeletal muscle caused collapse of the intermediate cisternae of the sarcoplasmic reticulum (SR), forming a pentalaminate structure by obi iterating the SR lumen, we demonstrated that the phenomenon involves the entire SR including the nuclear envelope and that it also occurs after treatment with other cations, including calcium (2,3,4).From these observations we have formulated a hypothesis which states that intracellular calcium taken up by the SR at the end of contraction causes the M rete to collapse at a certain threshold concentration as the first step in a subsequent centrifugal zippering of the free SR toward the junctional SR (JSR). This would cause a) bulk transport of SR contents, such as calcium and granular material (4) into the JSR and, b) electrical isolation of the free SR from the JSR.

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