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H Tinel

Publications and source records attributed to H Tinel.

5 recordsLinked to original sources
PubMed1997

Arachidonic acid as a second messenger for hypotonicity-induced calcium transients in rat IMCD cells.

In rat inner medullary collecting duct (IMCD) cells in primary culture, hypotonic stress induces Ca2+ transients consisting of an early peak phase caused by a Ca2+ release from intracellular stores and a subsequent plateau phase that involves Ca2+ entry from the extracellular milieu. In the present study, the mechanisms by which cell swelling is transduced into the Ca2+ release were investigated. The free intracellular Ca2+ concentration ([Ca2+]i) was measured using the fluorescent dye fura-2 and cell volume using a confocal laser scanning microscope. In control experiments, after reduction of extracellular osmolarity from 600 to 300 mosmol/l, by omission of sucrose, [Ca2+]i rapidly increased from 106 +/- 9 nmol/l to a peak value of 405 +/- 22 nmol/l (P </= 0.05) and thereafter reached a steady-state of 230 +/- 23 nmol/l. In low-Ca2+ conditions (10 nmol/l), the reduction of osmolarity evoked only a transient increase of [Ca2+]i by 182 +/- 11 nmol/l (P </= 0.05), which reflected Ca2+ release from intracellular stores. Hyposmotic stress had no effect on inositol 1,4,5-triphosphate (IP3) production measured by a [3H]IP3 radioreceptor assay. Preincubation with 100 micromol/l ETYA (a non-metabolisible derivative of arachidonic acid) reduced the Ca2+ response to hyposmotic stress under high and low Ca2+ conditions (87 and 85% inhibition respectively) as well as the regulatory volume decrease (RVD). Extracellular application of arachidonic acid in isotonic medium led to an increase in [Ca2+]i under high and low Ca2+ conditions. Pretreatment of IMCD cells with 50 microg/ml D609 (a phosphatidylcholine-directed phospholipase C inhibitor) or with 200 micromol/l propranolol (a phosphatidate phosphohydrolase inhibitor) reduced the hypotonic Ca2+ response more strongly than pretreatment with 5 micromol/l BPhB (a phospholipase A2 inhibitor). The Ca2+ response was also suppressed after preincubation with 200 micromol/l RHC 80267 (a diacylglycerol lipase inhibitor). Preincubation with 50 ng/ml pertussis toxin (a G-protein inhibitor) reduced the transient component of the Ca2+ response partially. We conclude that G-proteins, phosphatidylcholine-directed phospholipase C, phospholipase A2, diacylglycerol lipase and arachidonic acid, but not IP3, are involved in the mechanisms by which Ca2+ is released from the intracellular stores during RVD in IMCD cells.

Animals↗
PubMed1996

Osmoregulation in the renal papilla: membranes, messengers and molecules.

This contribution summarizes recent progress in the understanding of the molecular basis of the release of organic osmolytes that occurs when inner medullary cells are confronted with a drop in osmolarity in their environment. For sorbitol release across the basolateral membrane an increase in intracellular calcium seems to be the prominent signal, initiated by G-protein activation, followed by phosphatidylcholine phospholipase activation and generation of arachidonic acid. The increase in betaine permeability is also G-protein dependent but calcium independent, and is restricted to the basal-lateral cell face. Myo-inositol and glycerophosphorylcholine efflux are calcium and G-protein independent and occur both across the apical and basolateral membrane, although to a different extent. Taurine release is also calcium and G-protein independent; a swelling-activated anion channel at the basolateral membrane represents the major efflux pathway.

Animals↗
PubMed1994

Intracellular Ca2+ release and Ca2+ influx during regulatory volume decrease in IMCD cells.

Volume changes and cytosolic Ca2+ concentration ([Ca2+]i) of inner medullary collecting duct (IMCD) cells under hypotonic stress were monitored by means of confocal laser scanning microscopy and fura 2 fluorescence, respectively. Reduction of extracellular osmolality from 600 to 300 mosmol/kgH2O by omission of sucrose led to an increase in cell volume within 1 min to 135 +/- 3% (n = 9), followed by a partial regulatory volume decrease (RVD) to 109 +/- 2% (n = 9) within the ensuring 5 min. In parallel, [Ca2+]i rose from 145 +/- 9 to 433 +/- 16 nmol/l (n = 9) and thereafter reached a lower steady state of 259 +/- 9 nmol/l. Under low-Ca2+ conditions (10 nmol/l) RVD was not impeded and reduction of osmolality evoked only a transient increase of [Ca2+]i by 182 +/- 22 nmol/l (n = 6). Preincubation with 100 mumol/l 8-(N,N-diethylamino)octyl-3,4,5-trimethoxy-benzoate hydrochloride (TMB-8) or 20 mmol/l caffeine, both effective inhibitors of Ca2+ release from intracellular stores, in low Ca2+ as well as in high Ca2+, inhibited the Ca2+ response and abolished RVD. The temporal relationship between Ca2+ release from intracellular stores and Ca2+ entry was analyzed by determining fura 2 quenching, using Mn2+ as a substitute for external Ca2+. Intracellular Ca2+ release preceded Mn2+ influx by 17 +/- 3 s (n = 10). Mn2+ influx persisted during the whole period of exposure to hypotonicity, indicating that there is no time-dependent Ca2+ channel inactivation. Preincubation with TMB-8 or caffeine reduced Mn2+ influx to the control level, indicating that activation of Ca2+ channels in the plasma membrane occurs via intracellular Ca2+ release.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMedDate not supplied

Role of G-proteins in the regulation of organic osmolyte efflux from isolated rat renal inner medullary collecting duct cells.

Hypotonic shock (change of osmolality from 600 mosmol to 300 mosmol by lowering NaCl concentration) increases the release of organic osmolytes from isolated inner medullary collecting duct (IMCD) cells in the following sequence: taurine > betaine > sorbitol > myo-inositol > glycerophosphorylcholine (GPC). The role of G-proteins in regulating the hypotonicity-induced efflux was analysed by exposing cells to various concentrations of a G-protein inhibitor, pertussis toxin (PTX; 20-200 ng/ml), and a Gialpha-protein stimulator, mastoparan (10-50 microM). PTX diminished the hypotonic release of sorbitol and betaine by 43.2+/-9. 5% and 32.2+/-7.8% (n = 5), respectively. Efflux of GPC, myo-inositol and taurine was not significantly altered. Mastoparan (10 microM) increased osmolyte release under isotonic conditions such that release of betaine was increased 3.8-fold and that of sorbitol 2.1-fold, while GPC, myo-inositol and taurine effluxes were only slightly augmented. Under hypotonic conditions, mastoparan stimulated betaine release (1.86+/-0.2-fold, n = 5) but not that of sorbitol. As tested in connection with sorbitol and betaine release, the effect of mastoparan was abolished by PTX, but not the A23187-evoked sorbitol release. Like mastoparan, arachidonic acid increased the release of sorbitol and betaine under isotonic conditions, but under hypotonic conditions it only increased the release of betaine. As to the role of intracellular Ca2+, hypotonic shock evoked an intracellular Ca2+ peak which could be prevented by PTX. Mastoparan increased intracellular Ca2+ under isotonic conditions, whether the extracellular Ca2+ concentration was low or high. The results indicate that G-proteins are involved in regulating sorbitol and betaine efflux from IMCD cells. The G-proteins regulating sorbitol release are probably involved in generating the proper intracellular Ca2+ signal. Betaine efflux, which is independent of intracellular Ca2+, might be regulated by a G-protein-stimulated release of arachidonic acid. Thus, probably several G-proteins are involved in controlling organic osmolyte efflux from IMCD cells.

Animals↗