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Sahai A, Ganguly PK. Observations on atrial natriuretic peptide, sympathetic activity and renal Ca2+ pump in diabetic and hypertensive rats. Clin Auton Res 1993; 3:137-43. [PMID: 8391886 DOI: 10.1007/bf01818999] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
The relationship between atrial natriuretic peptide (ANP) and peripheral sympathetic nervous system function was studied in diabetic and hypertensive rats. Animals were studied in diabetic and hypertensive rats. Animals were divided into four groups: control, diabetic, hypertensive and diabetic plus hypertensive. Diabetes was induced by streptozotocin (65 mg/kg) injection and hypertension by abdominal aortic constriction. Studies were performed at 1 and 6 weeks. Plasma ANP was increased at 1 week in all groups except controls. Noradrenaline turnover, an index of sympathetic activity in kidney, was attenuated in all pathological groups unlike controls. These changes were associated with increased activity of Ca2++Mg2+ ATPase, which is known to serve as a Ca2+ pump in kidney cortex basolateral membrane. In contrast, at 6 weeks, Ca2++Mg2+ ATPase was significantly decreased only in the diabetic plus hypertensive group which also showed signs of congestive heart failure, increased sympathetic activity and decreased plasma ANP levels. Intracerebral microdialysis of the extracellular space around the paraventricular nucleus (PVN) of the hypothalamus showed a decreased concentration of ANP in the diabetic plus hypertensive group. Infusion of ANP and pentolinium, a ganglionic blocker in diabetic plus hypertensive Ca2+ restored pump activity towards control values; ANP alone had no effect. Our results indicate decreased plasma ANP levels, increased sympathetic drive and a depressed kidney Ca2+ pump in diabetic plus hypertensive rats with heart failure. The relationships between these factors, and the potential modulating role of ANP is discussed.
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Affiliation(s)
- A Sahai
- Division of Cardiovascular Sciences, St Boniface General Hospital Research Centre, Winnipeg, Manitoba, Canada
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52
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Bindels RJ, Dempster JA, Ramakers PL, Willems PH, van Os CH. Effect of protein kinase C activation and down-regulation on active calcium transport. Kidney Int 1993; 43:295-300. [PMID: 8441225 DOI: 10.1038/ki.1993.46] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Active transcellular Ca2+ transport in primary cultures of the rabbit kidney collecting system has been shown to be responsive to PTH through activation of protein kinase A (PKA). The present study investigates an additional regulatory pathway activated by protein kinase C (PKC). Cells from rabbit kidney connecting tubules and cortical collecting ducts were isolated by immunodissection and subsequently cultured on permeable filters. Incubation of cultured cells with the PKC activator, 12-O-tetradecanoylphorbol 13-acetate (TPA, 10(-8) to 10(-6) M) had a dual effect on active transcellular Ca2+ transport. Short-term incubation increased membrane-associated PKC activity within 10 minutes and decreased active transcellular Ca2+ transport dose-dependently (IC50 = 3.4 +/- 0.4 nM), with a maximal inhibition of 74 +/- 3%. TPA (10(-7) M) concomitantly inhibited the amiloride-sensitive transepithelial potential difference (p.d.) and short-circuit current across the monolayers. After prolonged exposure to TPA, total cellular PKC activity was down-regulated, resulting in a maximal 65 +/- 5% reduction after one hour. Interestingly, this latter event was temporally separated from a gradual return of both Ca2+ absorption rate and transepithelial p.d. to control levels occurring over 96 and 48 hours, respectively, of further incubation with TPA. The inhibitor of protein kinase activity, staurosporine (10(-7) M), when present during incubation with submaximal concentration of TPA (10(-8) M) partly prevented the TPA-induced inhibition of Ca2+ absorption from 54 +/- 4 to 27 +/- 3%. This study demonstrates for the first time that, in addition to PKA, activation of PKC plays a regulatory role in transcellular Ca2+ reabsorption in the renal collecting system.
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Affiliation(s)
- R J Bindels
- Department of Physiology, University of Nijmegen, The Netherlands
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53
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Hanaoka K, Sakai O, Imai M, Yoshitomi K. Mechanisms of calcium transport across the basolateral membrane of the rabbit cortical thick ascending limb of Henle's loop. Pflugers Arch 1993; 422:339-46. [PMID: 8382363 DOI: 10.1007/bf00374289] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Although net Ca2+ absorption takes place in the thick ascending limb of Henle's loop, detailed mechanisms are unknown. Because it has been reported that the Ca2+ entry step across the luminal membrane is mediated by Ca2+ channels inserted by stimulation with parathyroid hormone, we studied the mechanism of Ca2+ transport across the basolateral membrane of rabbit cortical thick ascending limb (CTAL) perfused in vitro by using microscopic fluorometry of cytosolic Ca2+ ([Ca2+]i) with fura-2. The resting [Ca2+]i in this segment was 49.8 +/- 4.5 nmol/l. Neither Na+ removal from the bathing solution nor addition of ouabain (0.1 mmol/l) to the bath increased [Ca2+]i, indicating that a Na+/Ca2+ exchanger in the basolateral membrane may not contribute in any major way to [Ca2+]i of CTAL. To confirm our technical accuracy, similar protocols were conducted in the connecting tubule, where the existence of a Na+/Ca2+ exchanger has been reported. In this segment, Na+ removal from the bath increased cell Ca2+ from 148.6 +/- 6.4 nmol/l to 647.6 +/- 132.0 nmol/l, confirming the documented fact. [Ca2+]i in the CTAL was markedly increased when 1 mmol/l NaCN was added to the bath in the absence of glucose. Calmodulin inhibitors (trifluoperazine or W-7) increased [Ca2+]i. When the bath pH was made alkaline, [Ca2+]i was also increased. This response was abolished when Ca2+ was eliminated from the bath, indicating that the Ca2+ entry across the basolateral membrane is dependent on bath pH. Increase in [Ca2+]i induced by an alkaline bath was inhibited by increased the bath K+ from 5 nmol/l to 50 mmol/l, suggesting that the Ca2+ entry system is voltage-dependent.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- K Hanaoka
- Second Department of Internal Medicine, Jikei University School of Medicine, Tokyo, Japan
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54
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Arita Y, Kimura T, Ogami Y, Nawata H. Phorbol ester attenuates inositol 1,4,5-trisphosphate-induced Ca2+ release in electropermeabilized rat pancreatic acini. RESEARCH IN EXPERIMENTAL MEDICINE. ZEITSCHRIFT FUR DIE GESAMTE EXPERIMENTELLE MEDIZIN EINSCHLIESSLICH EXPERIMENTELLER CHIRURGIE 1992; 192:295-303. [PMID: 1332151 DOI: 10.1007/bf02576286] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
To investigate the mechanism of inositol trisphosphate (IP3)-induced Ca2+ release from the internal Ca2+ store, we examined the effects of heparin, phorbol ester and cyclic nucleotides on Ca2+ release induced by carbachol or inositol 1,4,5-trisphosphate (1,4,5-IP3). For monitoring changes of Ca2+ we used the fluorescent indicator, fura-2, in electropermeabilized rat pancreatic acini. An amount of 100 micrograms/ml heparin inhibited the Ca2+ release induced by 1 microM 1,4,5-IP3 in permeabilized acini. Pretreatment with 12-O-tetradecanoyl-phorbol-13-acetate (TPA) for 10 min reduced the release of Ca2+ induced by 10 microM carbachol and 1 microM 1,4,5-IP3 in permeabilized acini. Staurosporine, a protein kinase C inhibitor, blocked the inhibitory effect of TPA. Cytosolic calcium concentration was restored by staurosporine in TPA-treated acini. Although cyclic AMP exaggerated the amylase release induced by carbachol, cyclic AMP and cyclic GMP had no effect on the carbachol-induced release of Ca2+ in permeabilized acini. These findings suggest that protein kinase C may act at the level of the IP3 receptors or the IP3-operated Ca2+ channels of the internal Ca2+ store and indicate that cyclic nucleotides do not affect the IP3-induced release of Ca2+ in rat pancreatic acini.
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Affiliation(s)
- Y Arita
- Third Department of Internal Medicine, Faculty of Medicine, Kyushu University, Fukuoka, Japan
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55
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Leinders T, Vijverberg HP. Ca2+ dependence of small Ca(2+)-activated K+ channels in cultured N1E-115 mouse neuroblastoma cells. Pflugers Arch 1992; 422:223-32. [PMID: 1488280 DOI: 10.1007/bf00376206] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Single-channel properties of Ca(2+)-activated K+ channels have been investigated in excised membrane patches of N1E-115 mouse neuroblastoma cells under asymmetric K+ concentrations at 0 mV. The SK channels are blocked by 3 nM external apamin, are unaffected by 20 mM external tetraethylammonium (TEA) and have a single-channel conductance of 5.4 pS. The half-maximum open probability and opening frequency of SK channels are observed at 1 microM internal Ca2+. Concentration/effect curves of these parameters are very steep with exponential slope factors between 7 and 13. Open-time distributions demonstrate the existence of at least two open states. The mean short open time increases with [Ca2+]i, whereas the mean long open time is independent of [Ca2+]i. At low [Ca2+]i the short-lived open state predominates. At saturating [Ca2+]i the number of long-lived openings is more enhanced than the number of short-lived openings and both open states occur equally frequently. The opening frequency as well as the open times of SK channels are independent of the membrane potential in the range of -16 to +40 mV. The results indicate that activation of K+ current through SK channels is mainly determined by the Ca(2+)-dependent single-channel opening frequency. BK channels in N1E-115 cells are insensitive to 100 nM external apamin, are sensitive to external TEA in the millimolar range and have a single-channel conductance of 98 pS. Half-maximum open probability and opening frequency of the BK channel are observed at 7.5-21 microM internal Ca2+. The slope factors of concentration/effect curves range between 1.7 and 2.9. As the BK channel open time is markedly enhanced at raised [Ca2+]i, the Ca2+ dependence of the current through BK channels is determined by the single-channel opening frequency as well as the open time. SK as well as BK channels appear to be clustered and interact in a negative cooperative manner in multiple channel patches. The differences in Ca2+ dependence suggest that BK channels are activated by a local high [Ca2+]i associated with Ca2+ influx, whereas SK channels may be activated by Ca2+ released from internal stores as well.
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Affiliation(s)
- T Leinders
- Research Institute of Toxicology, University of Utrecht, The Netherlands
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56
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Leinders T, van Kleef RG, Vijverberg HP. Divalent cations activate small- (SK) and large-conductance (BK) channels in mouse neuroblastoma cells: selective activation of SK channels by cadmium. Pflugers Arch 1992; 422:217-22. [PMID: 1488279 DOI: 10.1007/bf00376205] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Effects of Cd2+, Co2+, Fe2+ and Mg2+ (1 microM and 100 microM) and Pb2+ (1 microM and 90 microM) on single-channel properties of the small-conductance (SK) and large-conductance (BK) Ca(2+)-activated K+ channels were investigated in inside-out patches of N1E-115 mouse neuroblastoma cells. Cd2+, Co2+ and Pb2+, but not Fe2+ and Mg2+, cause SK channel opening. The potency of the metals in enhancing the SK channel-open probability follows the sequence Cd2+ approximately Pb2+ > Ca2+ > Co2+ >> Mg2+, Fe2+. The four metals that cause SK channel opening are equipotent in enhancing the opening frequency of SK channels. The BK channel is activated by Pb2+ and Co2+, whereas Cd2+, Fe2+ and Mg2+ are ineffective. The potency of the metals in enhancing BK channel-open probability, open time and opening frequency follows the sequence Pb2+ > Ca2+ > Co2+ >> Cd2+, Mg2+, Fe2+. The results show that SK channels are much more sensitive to Cd2+ than BK channels and indicate that Cd2+ is a selective agonist of SK channels. It is concluded that the various metal ions bind to the same regulatory site(s) at which Ca2+ activates the SK and BK channels under physiological conditions. The different potency sequences of metal ions with respect to BK and SK channel activation indicate that the regulatory sites of these Ca(2+)-activated K+ channels have distinct chemical and physical properties.
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Affiliation(s)
- T Leinders
- Research Institute of Toxicology, University of Utrecht, The Netherlands
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57
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Leinders T, van Kleef RG, Vijverberg HP. Single Ca(2+)-activated K+ channels in human erythrocytes: Ca2+ dependence of opening frequency but not of open lifetimes. BIOCHIMICA ET BIOPHYSICA ACTA 1992; 1112:67-74. [PMID: 1420271 DOI: 10.1016/0005-2736(92)90255-k] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Using the patch-clamp technique single-channel properties of Ca(2+)-activated K+ (CaK) channels were investigated in inside-out membrane patches of human erythrocytes. In a physiological K+ gradient (5 mM K+ externally: 150 mM K+ internally) the single CaK channel conductance is 15 pS in the membrane potential range of -40 to +40 mV. The channel open probability, opening frequency and open and closed time distributions are voltage-independent. The open probability and the opening frequency of the CaK channel depend on [Ca2+]i and increase between 0.5 and 60 microM Ca2+ from approx. 10% to 90% of the maximum value obtained at 115 microM. The relation between open probability and [Ca2+]i can be described by a sigmoid concentration-effect curve with an EC50 of 4.7 microM and a slope factor of 1. Independent of [Ca2+]i open time distributions yield two time constants of 5.3 and 22 ms. The relative amplitudes of the fast and slow components of the open time histogram as well as the maximum open probability and the maximum opening frequency of CaK channels vary considerably. In addition, CaK channels in multiple channel patches are highly interdependent. It is concluded that the Ca(2+)-dependence of CaK channels in human erythrocytes is due to the modulation of opening frequency by internal Ca2+. The results are consistent with a classical receptor-agonist model in which ligand interaction kinetics are much faster than channel gating.
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Affiliation(s)
- T Leinders
- Research Institute of Toxicology, University of Utrecht, Netherlands
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58
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Leinders T, van Kleef RG, Vijverberg HP. Distinct metal ion binding sites on Ca(2+)-activated K+ channels in inside-out patches of human erythrocytes. BIOCHIMICA ET BIOPHYSICA ACTA 1992; 1112:75-82. [PMID: 1420273 DOI: 10.1016/0005-2736(92)90256-l] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Effects of Cd2+, Co2+, Pb2+, Fe2+ and Mg2+ (1-100 microM) on single-channel properties of the intermediate conductance Ca(2+)-activated K+ (CaK) channels were investigated in inside-out patches of human erythrocytes in a physiological K+ gradient. Cd2+, Co2+ and Pb2+, but not Fe2+ and Mg2+, were able to induce CaK channel openings. The potency of the metals to open CaK channels in human erythrocytes follows the sequence Pb2+, Cd2+ > Ca2+ > or = Co2+ >> Mg2+, Fe2+. At higher concentrations Pb2+, Cd2+ and Co2+ block the CaK channel by reducing the opening frequency and the single-channel current amplitude. The potency of the metals to reduce CaK channel opening frequency follows the sequence Pb2+ > Cd2+, Co2+ >> Ca2+, which differs from the potency sequence Cd2+ > Pb2+, Co2+ >> Ca2+ to reduce the unitary single-channel current amplitude. Fe2+ reduced the channel opening frequency and enhanced the two open times of CaK channels activated by Ca2+, whereas up to 100 microM Mg2+ had no effect on any of the measured single-channel parameters. It is concluded that the activation of CaK channels of human erythrocytes by various metal ions occurs through an interaction with the same regulatory site at which Ca2+ activates these channels. The different potency orders for the activating and blocking effects suggest the presence of at least one activation and two blocking sites. A modulatory binding site for Fe2+ exists as well. In addition, the CaK channels in human erythrocytes are distinct from other subtypes of Ca(2+)-activated K+ channels in their sensitivity to the metal ions.
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Affiliation(s)
- T Leinders
- Research Institute of Toxicology, University of Utrecht, Netherlands
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59
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Sugihira N, Aoki Y, Suzuki KT. ATP-dependent strontium uptake by basolateral membrane vesicles from rat renal cortex in the absence or presence of calcium. Biol Trace Elem Res 1992; 34:45-54. [PMID: 1382521 DOI: 10.1007/bf02783897] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
ATP-dependent Sr2+ transport was examined in vitro using basolateral membrane (BLM) vesicles isolated from rat renal cortex to clarify the discrimination mechanisms between strontium (Sr) and calcium (Ca) in renal tubules during reabsorption. ATP-dependent Sr2+ uptake and Ca2+ uptake were observed in renal BLM vesicles and were inhibited by vanadate. Hill plots indicate similar kinetic behavior for Ca2+ and Sr2+ uptake. The apparent Km and Vmax of ATP-dependent Sr2+ uptake were both higher than those for Ca2+ uptake. ATP-dependent Sr2+ uptake by BLM vesicles diminished in the presence of 0.1 microM Ca2+ and was more markedly inhibited by 1 microM Ca2+. Hill plots of Sr2+ uptake data with and without 0.1 microM Ca2+ showed that the cooperative behavior of Sr2+ uptake was not changed by Ca2+. In the presence of 0.1 microM Ca2+, the affinity of the transport system for Sr2+ and the velocity of Sr2+ uptake in the BLM were both decreased. However, the rate of Ca2+ uptake was not diminished by Sr2+ concentrations of less than 1.6 microM. These results suggest that Ca2+ is preferentially transported in the renal cortex BLM when Ca2+ and Sr2+ are present at the same time.
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Affiliation(s)
- N Sugihira
- National Institute for Environmental Studies, Ibaraki, Japan
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60
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Kansen M, Keulemans J, Hoogeveen AT, Scholte B, Vaandrager AB, van der Kamp AW, Sinaasappel M, Bot AG, de Jonge HR, Bijman J. Regulation of chloride transport in cultured normal and cystic fibrosis keratinocytes. BIOCHIMICA ET BIOPHYSICA ACTA 1992; 1139:49-56. [PMID: 1377032 DOI: 10.1016/0925-4439(92)90081-w] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Cultured normal (N) cystic fibrosis (CF) keratinocytes were evaluated for their Cl(-)-transport properties by patch-clamp-, Ussing chamber- and isotopic efflux-measurements. Special attention was paid to a 32 pS outwardly rectifying Cl- channel which has been reported to be activated upon activation of cAMP-dependent pathways in N, but not in CF cells. This depolarization-induced Cl- channel was found with a similar incidence in N and CF apical keratinocyte membranes. However, activation of this channel in excised patches by protein kinase (PK)-A or PK-C was not successful in either N or CF keratinocytes. Forskolin was not able to activate Cl- channels in N and CF cell-attached patches. The Ca(2+)-ionophore A23187 activated in cell-attached patches a linear 17 pS Cl- channel in both N and CF cells. This channel inactivated upon excision. No relationship between the cell-attached 17 pS and the excised 32 pS channel could be demonstrated. Returning to the measurement of Cl- transport at the macroscopic level, we found that a drastic rise in intracellular cAMP induced by forskolin did in N as well as CF cells not result in a change in the short-circuit current (Isc) or the fractional efflux rates of 36Cl- and 125I-. In contrast, addition of A23187 resulted in an increase of the Isc and in the isotopic anion efflux rates in N and CF cells. We conclude that Cl(-)-transport in cultured human keratinocytes can be activated by Ca2+, but not by cAMP-dependent pathways.
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Affiliation(s)
- M Kansen
- Department of Cell Biology I and Genetics, Erasmus University, Rotterdam, Netherlands
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61
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Verbost PM, Lafeber FP, Spanings FA, Aarden EM, Wendelaar Bonga SE. Inhibition of Ca2+ uptake in freshwater carp, Cyprinus carpio, during short-term exposure to aluminum. THE JOURNAL OF EXPERIMENTAL ZOOLOGY 1992; 262:247-54. [PMID: 1640197 DOI: 10.1002/jez.1402620303] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
In carp exposed to pH 5.2 in fresh water, the Ca2+ influx from the water is reduced by 31% when compared to fish in water of neutral pH. At pH 5.2, the Ca2+ influx but not Na+ uptake is decreased by aluminum (Al). Al reduces Ca2+ influx dose-dependently: a maximum 55% reduction was observed after 1-2 h exposure to 200 micrograms.1(-1) (7.4 microM) Al. Branchial Ca2+ efflux is less sensitive to Al and affected only by exposure for more than 1 h to high Al concentrations. Na+ influx is not affected by concentrations Al up to 400 micrograms.1(-1). Na+ efflux, similarly to Ca2+ efflux, increased when fish were exposed for more than 1 h to 400 micrograms.1(-1) Al.
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Affiliation(s)
- P M Verbost
- Department of Animal Physiology, Faculty of Science, University of Nijmegen, The Netherlands
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62
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Schoenmakers TJ, Klaren PH, Flik G, Lock RA, Pang PK, Bonga SE. Actions of cadmium on basolateral plasma membrane proteins involved in calcium uptake by fish intestine. J Membr Biol 1992; 127:161-72. [PMID: 1322993 DOI: 10.1007/bf00231504] [Citation(s) in RCA: 45] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
The inhibition of Ca(2+)-ATPase, (Na+ + K+)-ATPase and Na+/Ca2+ exchange by Cd2+ was studied in fish intestinal basolateral plasma membrane preparations. ATP driven 45Ca2+ uptake into inside-out membrane vesicles displayed a Km for Ca2+ of 88 +/- 17 nM, and was extremely sensitive to Cd2+ with an IC50 of 8.2 +/- 3.0 pM Cd2+, indicating an inhibition via the Ca2+ site. (Na+ + K+)-ATPase activity was half-maximally inhibited by micromolar amounts of Cd2+, displaying an IC50 of 2.6 +/- 0.6 microM Cd2+. Cd2+ ions apparently compete for the Mg2+ site of the (Na+ + K+)-ATPase. The Na+/Ca2+ exchanger was inhibited by Cd2+ with an IC50 of 73 +/- 11 nM. Cd2+ is a competitive inhibitor of the exchanger via an interaction with the Ca2+ site (Ki = 11 nM). Bepridil, a Na+ site specific inhibitor of Na+/Ca2+ exchange, induced an additional inhibition, but did not change the Ki of Cd2+. Also, Cd2+ is exchanged against Ca2+, albeit to a lesser extent than Ca2+. The exchanger is only partly blocked by the binding of Cd2+. In vivo cadmium that has entered the enterocyte may be shuttled across the basolateral plasma membrane by the Na+/Ca2+ exchanger. We conclude that intracellular Cd2+ ions will inhibit plasma membrane proteins predominantly via a specific interaction with divalent metal ion sites.
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Affiliation(s)
- T J Schoenmakers
- Department of Animal Physiology, Faculty of Science, University of Nijmegen, The Netherlands
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63
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Verhage M, Sandman H, Mosselveld F, van de Velde M, Hengst PA, Lopes da Silva FH, Ghijsen WE. Perfusion of Immobilized Isolated Nerve Terminals as a Model for the Regulation of Transmitter Release: Release of Different, Endogenous Transmitters, Repeated Stimulation, and High Time Resolution. J Neurochem 1992; 58:1313-20. [PMID: 1347777 DOI: 10.1111/j.1471-4159.1992.tb11344.x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
To study the release of neurotransmitters, i.e., the recruitment of transmitters for release and the regulation of the release process, isolated nerve terminals (synaptosomes) of the rat forebrain were immobilized in Sephadex gel inside a perfusion chamber. In this way, the following were achieved: (a) A very limited pressure stress was exerted on the synaptosomes, so that these remained viable for long periods (greater than 30 min) inside the chamber and did not elute from the chamber, which allowed long-term experiments with repeated stimulations; (b) estimation of the release of various endogenous transmitters, both in a Ca(2+)-dependent (exocytotic) and Ca(2+)-independent manner; (c) a step-like stimulation with depolarizing agents (rise time, 3-4 s) and a high time resolution (600-ms sampling); and (d) negligible reuptake of transmitter into the terminals or extracellular breakdown. It is concluded that this perfusion setup helps to provide new insights in the presynaptic stimulus-secretion coupling, co-transmission, and the exo-endocytosis cycle.
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Affiliation(s)
- M Verhage
- Department of Experimental Zoology, University of Amsterdam, The Netherlands
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64
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Bindels RJ, Ramakers PL, Dempster JA, Hartog A, van Os CH. Role of Na+/Ca2+ exchange in transcellular Ca2+ transport across primary cultures of rabbit kidney collecting system. Pflugers Arch 1992; 420:566-72. [PMID: 1614831 DOI: 10.1007/bf00374634] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Cells from connecting tubule and cortical collecting duct of rabbit kidney were isolated by immunodissection with mAb R2G9 and cultured on permeable filters. Confluent monolayers developed an amiloride-sensitive transepithelial potential difference of -50 +/- 1 mV (lumen negative) and a transepithelial resistance of 507 +/- 18 omega cm2. Transepithelial Ca2+ transport increased dose-dependently with apical [Ca2+] and, in solutions containing 1 mM Ca2+, the active transcellular Ca2+ transport rate was 92 +/- 2 nmol h-1 cm-2. Transcellular Ca2+ transport was dependent on basolateral Na+ (Nab+). Isoosmotic substitution of Nab+ for N-methylglucamine resulted in a concentration-dependent decrease in Ca2+ absorption, with maximal inhibition of 67 +/- 5%. A Hill plot of the Na(+)-dependence yielded a coefficient of 1.9 +/- 0.4, indicating more than one Na+ site on a Na(+)-dependent Ca2+ transport system. In addition, the absence of Cab2+ resulted in a significant increase in Ca2+ transport both in the presence and absence of Nab+. Added basolaterally, ouabain (0.1 mM) inhibited Ca2+ transport to the same extent as did Na(+)-free solutions, while bepridil (0.1 mM), an inhibitor of Na+/Ca2+ exchange, reduced Ca2+ transport by 32 +/- 6%. Methoxyverapamil, felodipine, flunarizine and diltiazem (10 microM) were without effect. Depolarisation of the basolateral membrane, by raising [K+]b to 60 mM, significantly decreased transcellular Ca2+ transport, which is indicative of electrogenic Na+/Ca2+ exchange. In conclusion, active Ca2+ transport in the collecting system of rabbit kidney is largely driven by basolateral Na+/Ca2+ exchange. However, a residual Ca2+ absorption of about 30% was always observed, suggesting that other Ca2+ transport mechanisms, presumably a Ca(2+)-ATPase, participate as well.
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Affiliation(s)
- R J Bindels
- Department of Physiology, University of Nijmegen, The Netherlands
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65
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Tsukamoto Y, Saka S, Saitoh M. Parathyroid hormone stimulates ATP-dependent calcium pump activity by a different mode in proximal and distal tubules of the rat. BIOCHIMICA ET BIOPHYSICA ACTA 1992; 1103:163-71. [PMID: 1309659 DOI: 10.1016/0005-2736(92)90070-3] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
A new technique was developed to isolate basolateral membrane vesicles individually from proximal and distal tubules of the rat cortex. This new technique enabled us to study differences in their kinetics and mechanisms of hormonal regulation of Ca pump between proximal and distal tubules. The Ca pump in distal tubule has very high affinity (42.6 nM Ca2+) and the one in proximal tubule has relatively low affinity (75.6 nM Ca2+). Parathyroidectomy (PTX) decreased the Vmax of Ca pump activity in proximal tubule (4.68 +/- 0.99 vs. 9.08 +/- 2.21 nmol 45Ca2+/min per mg protein BLMV, P less than 0.05), while it increased Km in distal tubule (93.1 +/- 11.0 vs. 35.1 +/- 16.1 nM Ca2+, P less than 0.05). Restoration of serum Ca2+ concentration by 1,25(OH)2D3 supplement could not reverse these changes by PTX in Ca pump activity in either the proximal or the distal tubule. In conclusion, this study strongly suggested that parathyroid hormone stimulated Ca pump activity by increasing the Vmax in proximal tubule and by increasing the affinity in distal tubule. 1,25(OH)2D3 does not have a direct effect on the basolateral membrane Ca pump activity.
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Affiliation(s)
- Y Tsukamoto
- Department of Medicine, Kitasato University School of Medicine, Kanagawa, Japan
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66
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Windhager EE, Frindt G, Milovanovic S. The role of Na-Ca exchange in renal epithelia. An overview. Ann N Y Acad Sci 1991; 639:577-91. [PMID: 1785887 DOI: 10.1111/j.1749-6632.1991.tb17356.x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Affiliation(s)
- E E Windhager
- Department of Physiology and Biophysics, Cornell University Medical College, New York, New York 10021
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67
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Schultz SG, Hudson RL. Biology Of Sodium‐Absorbing Epithelial Cells: Dawning of a New Era. Compr Physiol 1991. [DOI: 10.1002/cphy.cp060402] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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68
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Gioglio L, Rapuzzi G, Quacci D. Ca++- and Na+, K+-ATPase activities in the fungiform papilla of the tongue ofRana Esculenta (Anura Ranidae). J Morphol 1991; 210:117-131. [DOI: 10.1002/jmor.1052100203] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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69
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Rubio I, Torres M, Miras-Portugal MT, Sánchez-Prieto J. Ca(2+)-independent release of glutamate during in vitro anoxia in isolated nerve terminals. J Neurochem 1991; 57:1159-64. [PMID: 1680156 DOI: 10.1111/j.1471-4159.1991.tb08274.x] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The effects of in vitro anoxia on the release of glutamate in isolated nerve terminals were studied. The extra-synaptosomal concentration of glutamate ([Glu]ext) under aerobic conditions was 2.3 microM and increased to 4.9 microM after 10 min of anoxia. However, when synaptosomes were incubated in the presence of lactate plus pyruvate instead of glucose, to prevent anaerobic glycolysis, anoxia induced an eightfold increase in the [Glu]ext. The accumulation of glutamate in the external medium during anoxia was Ca2+ independent and insensitive to a significant reduction of the Ca(2+)-dependent release of the amino acid. These results indicate that a Ca(2+)-independent efflux of cytoplasmic glutamate occurs during in vitro anoxia in isolated nerve terminals.
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Affiliation(s)
- I Rubio
- Departamento de Bioquímica, Facultad de Veterinaria, Universidad Complutense, Madrid, Spain
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70
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Hanssen RG, Aarden EM, van der Venne WP, Pang PK, Wendelaar Bonga SE. Regulation of secretion of the teleost fish hormone stanniocalcin: effects of extracellular calcium. Gen Comp Endocrinol 1991; 84:155-63. [PMID: 1778405 DOI: 10.1016/0016-6480(91)90075-h] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The release in vivo and in vitro of stanniocalcin (STC) from the corpuscles of Stannius (CS) of the rainbow trout and the European eel was studied. Intraperitoneal injection of CaCl2 (2.45 mmol.kg-1 fish) leads to an elevation of both ionic and total calcium in the plasma and results in the release of STC from the CS into the blood. Release of STC in vitro is not affected at "physiological" (1.0-1.5 mM) or lower Ca2+ levels in the incubation medium. High levels of Ca2+ (2.5 mM and higher), however, stimulate the release of STC, in particular that of stored STC. We hypothesize that variations in extracellular Ca2+ in the normocalcaemic range do not directly regulate STC release.
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Affiliation(s)
- R G Hanssen
- Department of Animal Physiology, Faculty of Science, University of Nijmegen, The Netherlands
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71
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van de Put FH, De Pont JJ, Willems PH. GTP-sensitivity of the energy-dependent Ca2+ storage pool in permeabilized pancreatic acinar cells. Cell Calcium 1991; 12:587-98. [PMID: 1959126 DOI: 10.1016/0143-4160(91)90056-k] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Isolated rabbit pancreatic acinar cells, permeabilized by saponin treatment and incubated in the presence of 0.1 microM free Ca2+, accumulated 3.3 nmol of Ca2+/mg of acinar protein in an energy-dependent pool. Part of this energy-dependent pool could be released by GTP in a polyethylene glycol-dependent manner. The kinetics of GTP-induced release of Ca2+ showed a biphasic pattern with an initial rapid phase followed by a sustained slower phase. In contrast, IP3-induced release of Ca2+ was completed within 30 s following addition of IP3. No reuptake of Ca2+ was observed following GTP- or IP3-induced release of Ca2+. The GTP effect was independent of IP3 and not inhibited by Ca2+, indicating that the IP3-operated Ca2+ channel is not involved in GTP-induced release of Ca2+. The size of the IP3-releasable pool was not affected by GTP, indicating that GTP, when added to permeabilized acinar cells, does not promote the coupling between IP3-insensitive and IP3-sensitive Ca2+ accumulating organelles. Thus, in permeabilized acinar cells, GTP and IP3 act on different Ca2+ sequestering pools. Interestingly, however, comparison of the size of the GTP-releasable pool with that of the IP3-releasable pool for the cell preparations used in the present study, revealed an inversed relationship, indicating that at the time of permeabilization the GTP-releasable pool can be coupled to a greater or lesser extent to the IP3-releasable pool. This suggests that, in the intact cell, a GTP-dependent mechanism may exist that controls the size of the IP3-releasable pool by coupling IP3-insensitive to IP3-sensitive organelles. Moreover, this suggests that the extent of coupling is preserved during permeabilization.
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Affiliation(s)
- F H van de Put
- Department of Biochemistry, University of Nijmegen, The Netherlands
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72
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Dempster JA, van Hoek AN, de Jong MD, van Os CH. Glucose transporters do not serve as water channels in renal and intestinal epithelia. Pflugers Arch 1991; 419:249-55. [PMID: 1745600 DOI: 10.1007/bf00371103] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Glucose carriers have been shown to serve as water channels in macrophages and in oocytes injected with messenger ribonucleic acid (mRNA) encoding the glucose carrier protein (Fischbarg et al. The contribution, therefore, of glucose carriers to osmotic water permeability (Pf) in renal and intestinal epithelial cells was investigated. Pf of brush border membrane vesicles (BBMVs) and of basolateral membrane vesicles (BLMVs) was studied using stopped-flow spectrophotometry. Osmotic shrinkage of renal vesicles exhibited fast and slow components at 4 degrees C and 37 degrees C. The fast component could be inhibited by HgCl2 or dimethylsulphoxide (DMSO) at these temperatures, whereas the slow component was inhibited only at 4 degrees C. Osmotic shrinkage of intestinal BBMVs and BLMVs was homogeneous at 4 degrees C and 37 degrees C and was slightly inhibitable by HgCl2 or DMSO at 4 degrees C but not 37 degrees C. In both tissues, vesicle uptake of glucose was sensitive to HgCl2, but not to DMSO. Phlorizin and phloretin inhibited D-glucose uptake in BBMVs and BLMVs respectively, but had no significant effect on Pf. In membrane vesicles of kidney origin, Pf was tenfold higher than in membranes from intestine. This difference was not reflected by the phlorizin- and phloretin-sensitive D-glucose uptakes. Our study concludes that glucose transporters do not serve as water channels in kidney or intestine. Although membrane proteins contribute slightly to Pf at 4 degrees C, this contribution is insignificant at 37 degrees C. A membrane protein serving specifically as a water channel could only be demonstrated in renal cortical membranes.
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Affiliation(s)
- J A Dempster
- Department of Physiology, University of Nijmegen, The Netherlands
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73
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Sahai A, Ganguly PK. Congestive heart failure in diabetes with hypertension may be due to uncoupling of the atrial natriuretic peptide receptor-effector system in the kidney basolateral membrane. Am Heart J 1991; 122:164-70. [PMID: 1648301 DOI: 10.1016/0002-8703(91)90774-c] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Hypertension is known to potentiate the risk of congestive heart failure (CHF) in diabetic individuals. Receptor-effector systems for atrial natriuretic peptide (ANP), which is known to regulate intracellular calcium (Ca2+), were studied in the kidney during hypertensive-diabetic cardiomyopathy in rats. Animals were divided into four groups: control, diabetic (D), hypertensive (H), and diabetic plus hypertensive (D + H). Diabetes was induced by a streptozotocin (65 mg/kg) injection and hypertension was induced by abdominal aortic constriction; studies were done at 1 and 6 weeks. Plasma ANP was increased at 1 week in the D, H, and D + H groups. There was a significant increase in the activity of Ca2+ + magnesium (Mg2+) adenosine triphosphatase (ATPase), which acts as a Ca2+ pump, in the kidney basolateral membrane from D, H, and D + H group at the 1 week study. Ca2+ + Mg2+ ATPase, on the other hand, was significantly decreased in the D + H group only at 6 weeks. This was associated with a decrease in plasma ANP, an increase in the kidney ANP receptor number, and a decrease in guanylate cyclase activity. The response of the Ca2+ pump to ANP was also attenuated. Since ANP is known to mediate its cellular effects in part by increasing Ca2+ + Mg2+ ATPase, the observed changes in the D + H group may contribute to the development of nephropathy and CHF.
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Affiliation(s)
- A Sahai
- Department of Anatomy, St. Boniface General Hospital Research Centre, Faculty of Medicine, University of Manitoba, Winnipeg, Canada
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74
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Lafond J, Leclerc M, Brunette MG. Characterization of calcium transport by basal plasma membranes from human placental syncytiotrophoblast. J Cell Physiol 1991; 148:17-23. [PMID: 1650372 DOI: 10.1002/jcp.1041480103] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
We have studied the mechanisms involved in calcium (Ca2+) transport through the basal plasma membranes (BPM) of the syncytiotrophoblast cells from full-term human placenta. These purified membranes were enriched 25-fold in Na+/K(+)-adenosine triphosphate (ATPase), 37-fold in [3H] dihydroalprenolol binding sites, and fivefold in alkaline phosphatase activity compared with the placenta homogenates. In the absence of ATP and Mg2+, a basal Ca2+ uptake was observed, which followed Michaelis-Menten kinetics, with a Km Ca2+ of 0.18 +/- 0.05 microM and Vmax of 0.93 +/- 0.11 nmol/mg/min. The addition of Mg2+ to the incubation medium significantly decreased this uptake in a concentration-dependent manner, with a maximal inhibition at 3 mM Mg2+ and above. The Lineweaver-Burk plots of Ca2+ uptake in the absence and in the presence of 1 mM Mg2+ suggest a noncompetitive type of inhibition. Preloading the BPM vesicles with 5 mM Mg2+ had no significant effect on Ca2+ uptake, eliminating the hypothesis of a Ca2+/Mg2+ exchange mechanism. This ATP-independent Ca2+ uptake was not sensitive to 10(-6) M nitrendipine nor to 10(-4) M verapamil. An ATP-dependent Ca2+ transport was also detected in these BPM, whose Km Ca2+ was 0.09 +/- 0.02 microM and Vmax 3.4 +/- 0.2 nmoles/mg/3 min. This Ca2+ transport requires Mg2+, the optimal concentration of Mg2+ being approximately 1 mM. Preincubation of the membrane with 10(-6) M calmodulin strongly enhanced the initial ATP-dependent Ca2+ uptake. Finally, no Na+/Ca2+ exchange process could be demonstrated.
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Affiliation(s)
- J Lafond
- Maisonneuve-Rosemont Hospital, Montreal, Quebec, Canada
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75
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Timmermans JA, Kaune R, Bindels RJ, van Os CH. Quantification of Ca(2+)-ATPases in porcine duodenum. Effects of 1,25(OH)2D3 deficiency. BIOCHIMICA ET BIOPHYSICA ACTA 1991; 1065:177-84. [PMID: 1647820 DOI: 10.1016/0005-2736(91)90228-z] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Previous studies have identified a calmodulin-stimulated ATP-dependent Ca2+ pump as the major Ca2+ efflux pathway in enterocytes. Here, we developed methods to quantify the number of Ca2+ pumps in basolateral and intracellular membranes from porcine duodenum. By the use of a pig strain with a genetic defect in renal 1 alpha-hydroxylase, we were able to investigate the influence of 1,25(OH)2D3-deficiency on the number of Ca(2+)-ATPases in porcine duodenum. The amount of Ca(2+)-ATPase in isolated basolateral membranes was 5.5 +/- 0.7 micrograms/mg protein, while the Vmax of ATP-dependent Ca2+ transport into inside-out resealed basolateral membrane vesicles was 2.6 +/- 0.4 nmol/mg protein per min. From these data we estimated roughly about 95 x 10(3) plasma membrane Ca2+ pump sites per enterocyte. In addition, the amount of intracellular Ca(2+)-ATPase in microsomal fractions was 0.41 +/- 0.02 microgram/mg protein. Comparison of these parameters between control and rachitic animals showed that Ca2+ pump capacities in both basolateral membranes and microsomal fractions of porcine duodenum are not influenced by 1,25(OH)2D3-deficiency. In conclusion, stimulatory effects of 1,25(OH)2D3 on intestinal Ca2+ transport most likely result from specific effects on apical influx and facilitation of cytosolic Ca2+ diffusion by Ca(2+)-binding proteins and not from an increase in Ca2+ pumping capacity in basolateral membranes.
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Affiliation(s)
- J A Timmermans
- Department of Physiology, University of Nijmegen, The Netherlands
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76
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Abstract
Discrimination between strontium (Sr) and calcium (Ca) was examined in suckling rats and compared with that in older rats after weaning. Concentrations of Sr and Ca and the Sr/Ca ratios in serum and femur of 10-d old and 21-d old rats were determined. The Sr concentrations and Sr/Ca ratios in the serum and femur of 10-d old rats were lower than those of 21-d old rats, that could be explained by the fact that 10-d old rats ingested only maternal milk in which the Sr/Ca ratio was much lower than the laboratory diet. The relative ratios of Sr/Ca in serum and femur to that in the diet were found to be higher in 10-d old rats compared with those in 21-d old rats, and also higher than those in the older rats after weaning, as described in our previous publication. This result may reflect that discrimination between Sr and Ca during intestinal absorption is lacking in very young animals before weaning and develops after this age. Renal discrimination between Sr and Ca in the suckling rats at 10 d of age was evaluated by determining the relationship between the relative clearances of Ca and Sr. The mathematical model proposed by Walser and Robinson was applied on these results and the parameter for the equation, that is, the discrimination constant, was shown to be higher in 10-d old rats compared to those in young (7 wk of age) and adult (25 wk of age) rats. This result suggests that the discrimination of Sr in favor of Ca during the tubular reabsorptive process may not be fully developed in the very young rats before weaning.
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Affiliation(s)
- N Sugihira
- National Institute for Environmental Studies, Ibaraki, Japan
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77
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Jacobs WR, Sgambati M, Gomez G, Vilaro P, Higdon M, Bell PD, Mandel LJ. Role of cytosolic Ca in renal tubule damage induced by anoxia. THE AMERICAN JOURNAL OF PHYSIOLOGY 1991; 260:C545-54. [PMID: 2003577 DOI: 10.1152/ajpcell.1991.260.3.c545] [Citation(s) in RCA: 29] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Cytosolic free Ca (Caf) was measured in three different preparations of freshly prepared proximal tubules from the rabbit kidney during energy deprivation using fura-2. Isolated perfused tubules, tubules immobilized on glass cover slips, and tubules in suspension were subjected to inhibitors of oxidative phosphorylation ("chemical hypoxia"); the latter two preparations were also subjected to 40 min of anoxia. During normoxia, Caf ranged from 100 to 180 nM in all three preparations, and chemical hypoxia caused either no change or a small (30-100%) increase in Caf values. Subsequent addition of Ca ionophores increased Caf to 300-500 nM in the first 2 min and to greater than 1 microM after 15 min. In individual experiments, anoxia produced similar responses to those of chemical hypoxia, eliciting no average significant change in Caf, despite clear evidence for impaired respiration and plasma membrane damage after 40 min of anoxia. This lack of change in Caf was unrelated to "Ca buffering" by fura-2 or inactivation of the dye, since Caf increased to 666 +/- 59 nM upon addition of Ca ionophore during anoxia. These data suggest that increased Caf is not a prerequisite for cellular damage during anoxia in proximal renal tubules. Furthermore, no apparent alteration in plasma membrane permeability to Ca occurs before membrane disruption. Decreased ATP seems to initiate a series of Caf-independent events that cause irreversible injury.
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Affiliation(s)
- W R Jacobs
- Department of Cell Biology, Duke University Medical Center, Durham, North Carolina 27710
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78
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The Effects of Parathyroid Hormone (PTH) on Ca Transport. Nephrology (Carlton) 1991. [DOI: 10.1007/978-3-662-35158-1_157] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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79
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Penniston JT. Role of Ca2+ ATPase and Plasma Membrane Ca2+ Pump in Ca2+ Transport by the Mammalian Kidney. Nephrology (Carlton) 1991. [DOI: 10.1007/978-3-662-35158-1_39] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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80
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Wiener H, de Jong MD, van Os CH. Active Ca2+ transport systems in basolateral membranes from rabbit distal colon. JOURNAL OF INTERNAL MEDICINE. SUPPLEMENT 1990; 732:119-24. [PMID: 2143382 DOI: 10.1111/j.1365-2796.1990.tb01483.x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Active Na+ absorption by tight epithelia such as frog skin and distal colon share common features like feedback inhibition of cellular [Na+] on Na+ influx through amiloride-sensitive Na+ channels. It is postulated that the negative feedback of increasing cell [Na+] is mediated via a rise in cell [Ca2+]. In this model, cell [Na+] is coupled to cell [Ca2+] via a Na+/Ca2+ exchange system in the basolateral membrane. In the present study, the Ca2+ transporting systems in rabbit distal colon basolateral membranes were characterized. ATP-dependent Ca2+ uptake could be demonstrated in membrane vesicles from surface cells with the following kinetic parameters: Km = 0.09 microM Ca2+ and Vm = 3.8 nmol Ca2+ mg-1 protein min-1. The ATP-dependent Ca2+ transport was not responsive to ruthenium red and oxalate, suggesting a plasmalemmal origin. The addition of 75 mM Na+ to the uptake medium, 10 min after addition of ATP, did not release Ca2+ from the vesicles in significant amounts. In the absence of ATP, outwardly directed Na+ gradients were incapable of stimulating Ca2+ uptake. This study demonstrates that rabbit distal colon epithelium lacks a well-defined Na+/Ca2+ exchange system, and (Ca2+, Mg2+)-ATPase appears to be the sole Ca2+ extrusion system. Alternatives for the coupling of cell [Na+] to cell [Ca2+] are discussed.
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Affiliation(s)
- H Wiener
- Department of Physiology, University of Nijmegen, The Netherlands
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81
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Affiliation(s)
- D Rouse
- Department of Medicine, Baylor College of Medicine, Houston, Texas
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82
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Sahai A, Ganguly PK. Lack of response of (Ca2+ + Mg2+) ATPase to atrial natriuretic peptide in basolateral membranes from kidney cortex of chronic diabetic rats. Biochem Biophys Res Commun 1990; 169:537-44. [PMID: 2141467 DOI: 10.1016/0006-291x(90)90364-s] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Incubation of basolateral membranes obtained from control rat kidney cortex in the presence of atrial natriuretic peptide (ANP) increased (Ca2+ + Mg2+) ATPase activity in a dose-dependent manner. Such response was absent in membranes obtained from animals made diabetic by streptozotocin injection (65 mg/kg, iv). The differential responses in the ATPase activity were not due to changes in the affinity for Ca2+ and insulin treatment in the diabetic animals completely reversed the situation. Our data suggest that ANP may mediate its cellular effects in part by changes in cellular Ca2+ homeostasis in kidney cortex and the lack of response of (Ca2+ + Mg2+) ATPase to ANP in chronic diabetes may contribute to the development of intracellular Ca2+ overload and nephropathy.
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Affiliation(s)
- A Sahai
- Department of Anatomy, St. Boniface General Hospital Research Centre, University of Manitoba, Winnipeg, Canada
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83
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Tacnet F, Watkins DW, Ripoche P. Studies of zinc transport into brush-border membrane vesicles isolated from pig small intestine. BIOCHIMICA ET BIOPHYSICA ACTA 1990; 1024:323-30. [PMID: 2112950 DOI: 10.1016/0005-2736(90)90361-q] [Citation(s) in RCA: 55] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Zinc transport into brush-border membrane vesicles was investigated by measuring uptake rates at a very short incubation time (2 seconds), during the initial linear uptake. A divalent cation chelator (EGTA) was added to the stop and washout solutions in order to remove the zinc bound to the external surface of the vesicles. Under these conditions, we showed that zinc enters the vesicles by (1) a saturable carrier-mediated process, and (2) an unsaturable pathway. The kinetic parameters we calculated were an affinity of 0.215 +/- 0.039 mM, a Jmax of 17.2 +/- 1.7 nmol.min-1.(mg protein)-1 and an unsaturable constant of 0.025 +/- 0.006 (n = 6). The imposition of an outwardly directed K+ gradient (negative inside) did not affect the Jmax value of the zinc uptake but increased the Km value significantly. This suggests that, at least a portion of zinc which crosses the membrane does not do so in a cationic form. Zinc uptake was decreased or increased according to the nature of accompanying anions (Cl-, SO4(2)-, SCN-) in the absence of any membrane potential. With highly permeant anions such as thiocyanates, zinc uptake was considerably augmented, suggesting a movement of zinc in a complexed form involving the presence of negative species. We also showed that cadmium competitively inhibited the zinc uptake; we measured a Ki value of 0.21 mM, indicating a similar affinity of cadmium for the carrier as zinc itself. By contrast, the presence of calcium had little effect on zinc entry into vesicles. The calcium ionophore A23187 had only a slight stimulating effect on zinc uptake. These results indicate that zinc and calcium transports are probably independent of each other.
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Affiliation(s)
- F Tacnet
- Service de Biologie Cellulaire, Centre d'Etudes Nucléaires de Saclay, Gif-sur-Yvette, France
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84
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Kelley LK, Borke JL, Verma AK, Kumar R, Penniston JT, Smith CH. The calcium-transporting ATPase and the calcium- or magnesium-dependent nucleotide phosphatase activities of human placental trophoblast basal plasma membrane are separate enzyme activities. J Biol Chem 1990. [DOI: 10.1016/s0021-9258(19)39382-2] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
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85
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Willems PH, De Jong MD, De Pont JJ, Van Os CH. Ca2(+)-sensitivity of inositol 1,4,5-trisphosphate-mediated Ca2+ release in permeabilized pancreatic acinar cells. Biochem J 1990; 265:681-7. [PMID: 2306208 PMCID: PMC1133688 DOI: 10.1042/bj2650681] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Hormonal and phorbol ester pretreatment of pancreatic acinar cells markedly decreases the Ins(1,4,5)P3-induced release of actively stored Ca2+ [Willems, Van Den Broek, Van Os & De Pont (1989) J. Biol. Chem. 264, 9762-9767]. Inhibition occurred at an ambient free Ca2+ concentration of 0.1 microM, suggesting a receptor-mediated increase in Ca2(+)-sensitivity of the Ins(1,4,5)P3-operated Ca2+ channel. To test this hypothesis, the Ca2(+)-dependence of Ins(1,4,5)P3-induced Ca2+ release was investigated. In the presence of 0.2 microM free Ca2+, permeabilized cells accumulated 0.9 nmol of Ca2+/mg of acinar protein in an energy-dependent pool. Uptake into this pool increased 2.2- and 3.3-fold with 1.0 and 2.0 microM free Ca2+ respectively. At 0.2, 1.0 and 2.0 microM free Ca2+, Ins(1,4,5)P3 maximally released 0.53 (56%), 0.90 (44%) and 0.62 (20%) nmol of Ca2+/mg of acinar protein respectively. Corresponding half-maximal stimulatory Ins(1,4,5)P3 concentrations were calculated to be 0.5, 0.6 and 1.4 microM, suggesting that the affinity of Ins(1,4,5)P3 for its receptor decreases beyond 1.0 microM free Ca2+. The possibility that an inhibitory effect of sub-micromolar Ca2+ is being masked by the concomitant increase in size of the releasable store is excluded, since Ca2+ release from cells loaded in the presence of 0.1 or 0.2 microM free Ca2+ and stimulated at higher ambient free Ca2+ was not inhibited below 1.0 microM free Ca2+. At 2.0 and 10.0 microM free Ca2+, Ca2+, Ca2+ release was inhibited by approx. 30% and 75% respectively. The results presented show that hormonal pretreatment does not lead to an increase in Ca2(+)-sensitivity of the release mechanism. Such an increase in Ca2(+)-sensitivity to sub-micromolar Ca2+ is required to explain sub-micromolar oscillatory changes in cytosolic free Ca2+ by a Ca2(+)-dependent negative-feedback mechanism.
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Affiliation(s)
- P H Willems
- Department of Biochemistry, University of Nijmegen, The Netherlands
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86
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Levy J, Grunberger G, Karl I, Gavin JR. Effects of food restriction and insulin treatment on (Ca2+ + Mg2+)-ATPase response to insulin in kidney basolateral membranes of noninsulin-dependent diabetic rats. Metabolism 1990; 39:25-33. [PMID: 2136760 DOI: 10.1016/0026-0495(90)90143-z] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Insulin increases (Ca2+ + Mg2+)-ATPase activity in cell membranes of normal rats but fails to do so in membranes of non-insulin-dependent diabetic (NIDD) rats. The loss of regulatory effect of the hormone on the enzyme might contribute to the insulin resistance observed in the NIDD animals. To further test this hypothesis, the effects of insulin treatment and acute food restriction on the ability of insulin to regulate the ATPase activity in kidney basolateral membranes (BLM) of NIDD rats were studied. Although insulin levels in NIDD and control rats were similar, plasma glucose was higher in the NIDD rats (18.3 +/- 1.5 v 19.3 +/- 1.7 microU/mL and 236 +/- 32 v 145 +/- 3 mg/dL, respectively). Insulin treatment (2 U/100 g), which increased plasma insulin in the NIDD rats (47.8 +/- 11.5 microU/mL; P less than .05), did not decrease their glucose (221 +/- 25 mg/dL). Higher insulin dose (4 U/100 g) decreased glucose level in the NIDD rats (73 +/- 3 mg/dL; P less than .001) but increased their plasma insulin 10-fold (202.5 +/- 52.5 microU/mL). Acute food restriction decreased glucose levels in the NIDD rats to levels seen in controls (135 +/- 3 mg/dL), while their insulin decreased by half (8.5 +/- 1.0 microU/mL; P less than .05). Basal (Ca2+ + Mg2+)-ATPase activity in BLM of all diabetic rats was higher than in controls (P less than .05). None of the treatments reversed this defect.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- J Levy
- Division of Metabolism, Washington University School of Medicine, St. Louis, MO
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87
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Flik G, Schoenmakers TJ, Groot JA, van Os CH, Wendelaar Bonga SE. Calcium absorption by fish intestine: the involvement of ATP- and sodium-dependent calcium extrusion mechanisms. J Membr Biol 1990; 113:13-22. [PMID: 2137539 DOI: 10.1007/bf01869601] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Measurements of unidirectional calcium fluxes in stripped intestinal epithelium of the tilapia, Oreochromis mossambicus, in the presence of ouabain or in the absence of sodium indicated that calcium absorption via the fish intestine is sodium dependent. Active Ca2+ transport mechanisms in the enterocyte plasma membrane were analyzed. The maximum capacity of the ATP-dependent Ca2+ pump (Vm: 0.63 nmol.min-1.mg-1, Km:27 nM Ca2+) is calculated to be 2.17 nmol.min-1.mg-1, correcting for 29% inside-out oriented vesicles in the membrane preparation. The maximum capacity of the Na+/Ca2+ exchanger with high affinity for Ca2+ (Vm:7.2 nmol.min-1.mg-1, Km:181 nM Ca2+) is calculated to be 13.6 nmol.min-1.mg-1, correcting for 53% resealed vesicles and assuming symmetrical behavior of the Na+/Ca2+ exchanger. The high affinity for Ca2+ and the sixfold higher capacity of the exchanger compared to the ATPase suggest strongly that the Na+/Ca2+ exchanger will contribute substantially to Ca2+ extrusion in the fish enterocyte. Further evidence for an important contribution of Na+/Ca2+ exchange to Ca2+ extrusion was obtained from studies in which the simultaneous operation of ATP- and Na(+)-gradient-driven Ca2+ pumps in inside-out vesicles was evaluated. The fish enterocyte appears to present a model for a Ca2+ transporting cell, in which Na+/Ca2+ exchange activity with high affinity for Ca2+ extrudes Ca2+ from the cell.
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Affiliation(s)
- G Flik
- Department of Animal Physiology, Faculty of Science, University of Nijmegen, The Netherlands
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88
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Taniguchi S, Marchetti J, Morel F. Na/Ca exchangers in collecting cells of rat kidney. A single tubule fura-2 study. Pflugers Arch 1989; 415:191-7. [PMID: 2594475 DOI: 10.1007/bf00370591] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Single pieces of fura-2-loaded cortical collecting tubule (CCT) isolated either from normal or adrenalectomized (ADX) rats were superfused in vitro, and the cytosolic calcium concentration [( Ca2+]i) was calculated from fluorescence recordings. The effects of altering the sodium gradient across cell membranes were investigated. Switching external sodium from 164 mM to 27 mM (low [Na+]o) had little effect on [Ca2+]i in normal tubules (106 +/- 9 versus 101 +/- 9 nM, n = 15) whereas it resulted in a large peak of [Ca2+]i in CCT from ADX-rats (270 +/- 32 versus 135 +/- 11 nM, n = 21). Since CCT from ADX rats are known to have a reduced Na-pump activity, the effect of ouabain treatment on CCT from normal rats was also tested. When CCT from normal rats were exposed to 1 mM of ouabain in the presence of 164 mM of [Na+]o, [Ca2+]i increased only moderately (123 +/- 15 versus 111 +/- 11 nM, n = 13); when the low [Na+]o solution was applied to these ouabain-treated tubules, a large and transient increase in [Ca2+]i was obtained (287 +/- 38 versus 123 +/- 15 nM, n = 13). This response was absent with [Ca2+]o = 0. The data suggest the presence of 3 Na+/1 Ca2+ exchangers in cell membranes of rat CCT.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- S Taniguchi
- Laboratoire de Physiologie Cellulaire du Collège de France, UA219 du CNRS, Paris
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89
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Verhage M, Besselsen E, Lopes da Silva FH, Ghijsen WE. Ca2+-dependent regulation of presynaptic stimulus-secretion coupling. J Neurochem 1989; 53:1188-94. [PMID: 2570127 DOI: 10.1111/j.1471-4159.1989.tb07413.x] [Citation(s) in RCA: 72] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
In the present study, we have investigated the role of Ca2+ in the coupling of membrane depolarization to neurotransmitter secretion. We have measured (a) intracellular free Ca2+ concentration ([Ca2+]i) changes, (b) rapid 45Ca2+ uptake, and (c) Ca2+-dependent and -independent release of endogenous glutamate (Glu) and gamma-aminobutyric acid (GABA) as a function of stimulus intensity by elevating the extracellular [K+] to different levels in purified nerve terminals (synaptosomes) from rat hippocampus. During stimulation, Percoll-purified synaptosomes show an increased 45Ca2+ uptake, an elevated [Ca2+]i, and a Ca2+-dependent as well as a Ca2+-independent release of both Glu and GABA. With respect to both amino acids, synaptosomes respond on stimulation essentially in the same way, with maximally a fourfold increase in Ca2+-dependent (exocytotic) release. Ca2+-dependent transmitter release as well as [Ca2+]i elevations show maximal stimulation at moderate depolarizations (30 mM K+). A correlation exists between Ca2+-dependent release of both Glu and GABA and elevation of [Ca2+]i. Ca2+-dependent release is maximally stimulated with an elevation of [Ca2+]i of 60% above steady-state levels, corresponding with an intracellular concentration of approximately 400 nM, whereas elevations to 350 nM are ineffective in stimulating Ca2+-dependent release of both Glu and GABA. In contrast, Ca2+-independent release of both Glu and GABA shows roughly a linear rise with stimulus intensity up to 50 mM K+. 45Ca2+ uptake on stimulation also shows a continuous increase with stimulus intensity, although the relationship appears to be biphasic, with a plateau between 20 and 40 mM K+.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- M Verhage
- Department of Experimental Zoology, University of Amsterdam, The Netherlands
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90
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Felder CC, McKelvey AM, Gitler MS, Eisner GM, Jose PA. Dopamine receptor subtypes in renal brush border and basolateral membranes. Kidney Int 1989; 36:183-93. [PMID: 2528652 DOI: 10.1038/ki.1989.178] [Citation(s) in RCA: 80] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Dopamine (DA) modulates renal tubular sodium transport by actions at both brush border (BBM) and basolateral membranes (BLM). DA receptors have been demonstrated in proximal tubule but the subtype of DA receptor in either BBM or BLM has not been determined. DA-1 receptors were quantitated by the specific binding of 125I-SCH 23982, a DA-1 antagonist (defined by 20 microM SCH 23390, a DA-1 antagonist) and DA-2 receptors by the specific binding of 3H-methyl-spiroperidol or 3H-spiroperidol (defined by 30 microM trifluperidol, a predominantly DA-2 antagonist). The specific binding of 125I-SCH 23982 and 3H-methyl-spiroperidol or 3H-spiroperidol were saturable with time and ligand concentration and reversible. Analysis of Rosenthal plots by non-linear regression revealed a high affinity site and a very low affinity site for both BLM and BBM. Maximum receptor density was similar in BBM and BLM. Competition experiments with 125I-SCH 23982 revealed high and low affinity binding sites in both BBM and BLM. The high affinity site was characteristic of a DA-1 receptor. Competition experiments with 3H-spiroperidol were also suggestive of DA-2 receptors. DA-1 but not DA-2 drugs increased adenylate cyclase and phospholipase-C activities in both BBM and BLM. However, their effects were greater in BLM than BBM. We conclude that DA-1 and DA-2 receptors are present in both BBM and BLM in canine kidney. Renal DA-1 receptors are linked to stimulation of both adenylate cyclase and phospholipase-C activity.
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Affiliation(s)
- C C Felder
- Department of Pediatrics, Georgetown University Medical Center, Washington, DC
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91
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Willems PHGM, Van den Broek BAM, Van Os CH, De Pont JJHHM. Inhibition of inositol 1,4,5-trisphosphate-induced Ca2+ release in permeabilized pancreatic acinar cells by hormonal and phorbol ester pretreatment. J Biol Chem 1989. [DOI: 10.1016/s0021-9258(18)81723-9] [Citation(s) in RCA: 33] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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92
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Verbost PM, Flik G, Pang PK, Lock RAC, Wendelaar Bonga SE. Cadmium Inhibition of the Erythrocyte Ca2+ Pump. J Biol Chem 1989. [DOI: 10.1016/s0021-9258(18)83591-8] [Citation(s) in RCA: 74] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
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93
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Blitzer BL, Hostetler BR, Scott KA. Hepatic adenosine triphosphate-dependent Ca2+ transport is mediated by distinct carriers on rat basolateral and canalicular membranes. J Clin Invest 1989; 83:1319-25. [PMID: 2703534 PMCID: PMC303824 DOI: 10.1172/jci114018] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
To characterize and localize hepatic plasma membrane ATP-dependent Ca2+ transport and Na+/Ca2+ exchange, studies were performed using highly purified rat basolateral and canalicular membrane vesicles. ATP-dependent Ca2+ transport activity was present in vesicles from both domains, insensitive to azide, oligomycin, oxalate, calmodulin, and calmidazolium, and virtually abolished at pH 6.8. However, basolateral and canalicular transport differed significantly. While basolateral transport was markedly stimulated by 1 mM Mg2+, canalicular transport was Mg2+ independent. Basolateral transport was similar at pH 7.4 and 8.0 but canalicular activity was stimulated fourfold at pH 8.0. Both Ca2+ Km [1.4 +/- 0.1 (SE).10(-8) vs. 4.8 +/- 0.7.10(-8) M] and Vmax (3.6 +/- 0.1 vs. 9.0 +/- 0.6 nmol mg-1 protein min-1) were lower in basolateral than in canalicular vesicles. Basolateral transport was somewhat more nucleotide specific (for ATP) and sensitive to vanadate (IC50 130 vs. 500 microM, respectively) than was canalicular transport. Na+/Ca2+ exchange activity was not detected in membranes from either domain. These studies suggest that hepatic ATP-dependent Ca2+ transport is mediated by domain-specific carriers on the basolateral and canalicular membranes.
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Affiliation(s)
- B L Blitzer
- Department of Internal Medicine, University of Cincinnati College of Medicine, Ohio 45267
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94
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Hanai H, Liang CT, Cheng L, Sacktor B. Desensitization to parathyroid hormone in renal cells from aged rats is associated with alterations in G-protein activity. J Clin Invest 1989; 83:268-77. [PMID: 2492037 PMCID: PMC303671 DOI: 10.1172/jci113869] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Parathyroid hormone (PTH)-stimulated Na+/Ca2+ exchange activity, but not forskolin-sensitive Na+-dependent Ca2+ efflux, was blunted in renal cortical cells from aged rats. PTH-sensitive adenylate cyclase activity in renal membranes from senescent rats also declined, but forskolin-stimulated activity did not change. In addition, cholera toxin- and pertussis toxin-stimulated Na+-dependent Ca2+ efflux and cAMP formation were blunted in cells from aged animals. Further, cells from aged rats had decreased Gs-alpha and Gi-alpha proteins, as detected by ADP-ribosylation. These findings would be consistent with the proposal of an age-associated heterologous desensitization that involved the G-proteins. Serum concentrations of iPTH were increased in the old rat, suggesting that the desensitization to PTH in the aging rat represented an adaptive response to prolonged stimulation by the hormone. This hypothesis was supported by the findings that the attenuated PTH-sensitive Na+/Ca2+ exchange activity, cAMP formation, and adenylate cyclase activity in cells from old rats could be reversed by parathyroidectomy. The decreased label in cholera toxin-catalyzed ADP-ribosylated Gs-alpha and pertussis toxin catalyzed ADP-ribosylated Gi-alpha found in cells from aged rats was also largely negated by the surgery. In conclusion, the results suggest that the age-related blunting in the responses of renal cells to PTH was associated with a deficit in G-protein function and that this alteration could be reversed by removal of the parathyroid gland.
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Affiliation(s)
- H Hanai
- Laboratory of Biological Chemistry, National Institute on Aging, Baltimore, Maryland 21224
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95
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Murer H, Gmaj P, Steiger B, Hagenbuch B. Transport studies with renal proximal tubular and small intestinal brush border and basolateral membrane vesicles: vesicle heterogeneity, coexistence of transport system. Methods Enzymol 1989; 172:346-64. [PMID: 2747534 DOI: 10.1016/s0076-6879(89)72023-1] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
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96
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Chapter 6 The “Second” Sodium Pump and Cell Volume. ACTA ACUST UNITED AC 1989. [DOI: 10.1016/s0070-2161(08)60010-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
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97
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Ramachandran C, Brunette MG. The renal Na+/Ca2+ exchange system is located exclusively in the distal tubule. Biochem J 1989; 257:259-64. [PMID: 2920016 PMCID: PMC1135564 DOI: 10.1042/bj2570259] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
The movement of Ca2+ across the basolateral plasma membrane was determined in purified preparations of this membrane isolated from rabbit proximal and distal convoluted tubules. The ATP-dependent Ca2+ uptake was present in basolateral membranes from both these tubular segments, but the activity was higher in the distal tubules. A very active Na+/Ca2+ exchange system was also demonstrated in the distal-tubular membranes, but in proximal-tubular membranes this exchange system was not demonstrable. The presence of Na+ outside the vesicles gradually inhibited the ATP-dependent Ca2+ uptake in the distal-tubular-membrane preparations, but remained without effect in those from the proximal tubules. The activity of the Na+/Ca2+ exchange system in the distal-tubular membranes was a function of the imposed Na+ gradient. These results suggest that the major differences in the characteristics of Ca2+ transport in the proximal and in the distal tubules are due to the high activity of a Na+/Ca2+ exchange system in the distal tubule and its virtual absence in the proximal tubule.
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Affiliation(s)
- C Ramachandran
- Maisonneuve-Rosemont Research Center, Montreal, Quebec, Canada
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98
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Abstract
Diabetes mellitus and hypertension are both common diseases, especially with an increasingly aged population. Hypertension accelerates the development of diabetic retinopathy, nephropathy, and peripheral vascular disease in the diabetic patient. Diabetes represents a type of premature aging and hypertension in the diabetic patient is characterized by many of the same pathophysiologic properties seen in the elderly hypertensive patient.
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Affiliation(s)
- J R Sowers
- Division of Endocrinology, Wayne State University, School of Medicine, Detroit, Michigan
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99
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Different sensitivity to trypsin of the human platelet plasma and intracellular membrane Ca2+ pumps. J Biol Chem 1988. [DOI: 10.1016/s0021-9258(18)68332-2] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
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100
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Tosco M, Orsenigo MN, Esposito G, Faelli A. Ouabain-insensitive active sodium transport in rat jejunum: evidence from ATPase activities, Na uptake by basolateral membrane vesicles and in vitro transintestinal transport. Cell Biochem Funct 1988; 6:155-64. [PMID: 2970332 DOI: 10.1002/cbf.290060303] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
The basolateral membrane of the jejunal enterocyte of the rat was separated by self-orienting Percoll-gradient centrifugation and further purified from brush border contamination. Pellets were analysed for Mg-, Na- and (Na,K)-ATPase activities. The uptake of 0.02 M NaCl was also followed by the rapid micro-filtration technique. Transintestinal transport of fluid and electrolytes, and cell water, Na and K were determined in the in vitro everted and incubated jejunum. There is ouabain-insensitive Na-ATPase in addition to the well-known (Na,K)-ATPase in the basolateral membrane. These are differently inhibited by furosemide and ethacrynate. Na uptake by osmotically active basolateral membrane vesicles is enhanced by ATP and a further enhancement is obtained if there is intravesicular K. The ATP effect is inhibited differently by strophanthidin, furosemide and ethacrynate. In the everted sac preparation, transintestinal transport of Na and fluid still occurs when the Na/K pump is totally inhibited by ouabain. These experimental results suggest that there is also a ouabain-insensitive Na pump, different from the Na/K pump, in the basolateral membrane.
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Affiliation(s)
- M Tosco
- Dipartimento di Fisiologia e Biochimica Generali, Università di Milano, Italy
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