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P Westerlund

Publications and source records attributed to P Westerlund.

5 recordsLinked to original sources
PubMed1991

Intracellular cytosolic free calcium concentration in the macula densa and in ascending limb cells at different luminal concentrations of sodium chloride and with added furosemide.

The juxtaglomerular apparatus fulfils several important regulatory functions in the kidney, such as tubuloglomerular feedback (TGF) control and control of renin release. The macula densa (MD) cells sense the fluid load by perceiving the distal NaCl concentration via a Na-K-2Cl cotransport system in the luminal cell membrane. It has been proposed that macula densa cell activation may involve changes in intracellular cytosolic free calcium concentration ([Ca2+]i), as one link in the chain of events activating TGF or releasing renin. We therefore investigated the changes in the intracellular calcium concentrations with fura-2, using a video system, in macula densa cells, and compared them with the changes in the corresponding concentrations in the ascending limb of the loop of Henle (c-TAL). The results show that our technique for analysing intracellular cytosolic free calcium in isolated perfused tubules is valid for this purpose, and the Kd value obtained was similar to that found by Grynkiewicz et al. (1985). The intracellular cytosolic free calcium concentration was about 90 nM both in the macula densa and c-TAL cells, and the macula densa cell intracellular cytosolic free calcium concentration increased by about 20 nM when the tubular lumen was perfused with Na and Cl at low concentrations. No significant changes were noted when furosemide was added to the perfusion solutions. We consider it hardly likely that this small change in intracellular cytosolic free calcium concentration can be entirely responsible for full activation of renin release or full inactivation of the TGF control mechanism. It would seem that the signal transmission from the macula densa cells could occur by other routes than through activation of intracellular cytosolic free calcium concentration.

Animals↗
PubMed1991

Macula densa cell function.

Studies concerning the sensing step in the tubuloglomerular feedback (TGF) mechanism have been conflicting. To study this step, we measured macula densa (MD) cell volume and membrane potentials in the isolated perfused ascending limb of the loop of Henle with attached glomerulus with MD segments (cTAL-MD). Addition of furosemide reduced cell volume rapidly and the effect could be reversed on removal of the drug. From the time course of cell volume changes hydraulic conductivity could be measured both in the basolateral and apical cell membrane. It was found that the apical cell membrane constituted the main barrier for water flow with a low hydraulic conductance, while the basolateral hydraulic conductance was quite high. Measurements of the basolateral electrical potential in the MD cells have shown a mean electrical potential of -56 mV. This potential was hyperpolarized by the addition of furosemide, the Cl channel blocker NPPB, or during a reduction of luminal NaCl from 150 to 30 mM, and depolarized when bath Cl concentration was reduced from 150 to 30 mM. These results are consistent with the following model for electrolytes transported and similar to the one described in the cTAL [15]. In the luminal cell membrane there is an Na-K-2Cl cotransporter that takes these ions into the MD cells and there is a potassium recycling through a K channel. On the basolateral membrane side there is an Na-K pump and a Cl channel through which chloride is transported out of the MD cell. The Na-K pump activity seems to be only 1/40 of that in the cTAL cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Chloride concentration in macula densa and cortical thick ascending limb cells.

The Cl- transport through the macula densa (MD) cells is believed to be a link in the tubuloglomerular feedback (TGF) believed to be a link in the tubuloglomerular feedback (TGF) mechanism and MD-mediated renin release. One step in this transport is probably the electroneutral and furosemide-sensitive Na(+)-K(+)-2Cl- contransport on the luminal membrane of MD cells. Another step is transport through basolateral Cl- channels. In the present study the intracellular Cl- concentration, [Cl-]i, was measured in the MD and cortical thick ascending limb (cTAL) cells, and the concentration changes elicited by blocking the Na(+)-K(+)-2Cl- cotransport with furosemide or by lowering the luminal NaCl concentration determined. We also investigated the effects of blocking the basolateral Cl- channels. A preparation consisting of a segment of the cTAL, MD cells, and the attached glomerulus was dissected from rabbit kidneys. The preparation was loaded with the Cl(-)-sensitive fluorophore SPQ, and perfused by using the isolated and perfused tubule technique. The intracellular chloride concentration was determined with a video system using digital imaging that measured the intensity of the emitted SPQ fluorescence. The T 1/2 of the leakage of SPQ was found to be (197 +/- 60) min (n = 9). With 150 mM NaCl in the lumen and bath, [Cl-]i in MD cells was 47 +/- 13 mM (n = 8) and 54 +/- 13 mM (n = 5) in cTAL cells. When furosemide (10(-4) M) was added to the luminal perfusion, the MD cell [Cl-]i was reduced to 6 +/- 2 mM. The corresponding value in cTAL cells was 5 +/- 3 mM.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Optical studies on the action of furosemide on macula densa and cortical thick ascending limb cells. Intracellular calcium fluorescence measurements.

The present study shows the successful use of an optical technique that describes the application of both differential interference contrast (DIC) and fluorescence microscopy to the study of structure-function relationships in isolated perfused cTAL-MD segments of the nephron. Image-intensified video microscopy and digital image processing techniques were used to simultaneously and directly visualize and quantify [Ca+2]i in individual cTAL cells and MD cells. This study also indicates that no large changes in MD [Ca+2]i can be observed under maneuvers that are known to affect the autoregulatory mechanisms of single nephron glomerular filtration rate. Therefore, it is less likely that MD [Ca+2]i could be a link in the transmission of the signal from the MD cells to the rest of the cells in the juxtaglomerular apparatus for the release of the TGF mechanism and/or renin. Possibly some other mechanism like the electrolyte transport itself, that can alter the solute concentration and tonicity of the Goormaghtigh cell field (juxtaglomerular interstitium), may be the signal to proceed with the rest of the events developed by the juxtaglomerular apparatus to control single nephron glomerular filtration rate.

Animals↗