Modulation of active Ca2+ uptake by the islet-cell endoplasmic reticulum

Colca, Jerry R.; Kotagal, Nirmala; Lacy, Paul E.; McDaniel, Michael L.

doi:10.1042/bj2120113

Cited by 27 publications

(14 citation statements)

References 50 publications

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“…Calcium uptake into sarcoplasmic reticulum [1] and endoplasmic reticulum of various tissues [11,16,20,22,26,33,35,39,44,46,62] can be stimulated by oxalate. This is a characteristic feature of the endoplasmic reticulum, in contrast to calcium uptake into plasma membrane vesicles [30,62], due to the permeability of the endoplasmic reticulum to oxalate.…”

Section: Calcium-precipitating Anionsmentioning

confidence: 99%

“…Ca 2+ uptake is dependent upon monovalent cations in the endoplasmic reticulum of several tissues [11,22,26,39,40,62], as well as in the sarcoplasmic reticulum [13,17,25,36,37,58]. We have therefore investigated the influence of different cations such as Rb +, K +, Na +, Li + and choline + on nonmitochondrial calcium uptake into leaky isolated cells and in isolated endoplasmic reticulum vesicles prepared from these cells.…”

Section: Monoualent Cationsmentioning

confidence: 99%

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Characterization of calcium uptake into rough endoplamic reticulum of rat pancreas

et al. 1984

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ATP-dependent Ca2+ uptake into isolated pancreatic acinar cells with permeabilized plasma membranes, as well as into isolated endoplasmic reticulum prepared from these cells, was measured using a Ca2+ -specific electrode and 45Ca2+. Endoplasmic reticulum was purified on an isopycnic Percoll gradient and characterized by marker enzyme distribution. When compared to the total homogenate, the typical marker for the rough endoplasmic reticulum RNA was enriched threefold and the typical marker for the plasma membrane Na+,K+(Mg2+)ATPase was decreased 20-fold. When different fractions of the Percoll gradient were compared, 45Ca2+ uptake correlated with the RNA content and not with the Na+,K+(Mg2+)ATPase activity. The characteristics of nonmitochondrial Ca2+ uptake into leaky isolated cells and 45Ca2+ uptake into isolated endoplasmic reticulum were very similar: Calcium uptake was maximal at 0.3 and 0.2 mmol/liter free Mg2+, at 1 and 1 mmol/liter ATP, at pH 6.0 and 6.5, and free Ca2+ concentration of 2 and 2 mumol/liter, respectively. Calcium uptake decreased at higher free Ca2+ concentration. 45Ca2+ uptake was dependent on monovalent cations (Rb+ greater than K+ greater than Na+ greater than Li+ greater than choline+) and different anions (Cl- greater than Br- greater than SO4(2-) greater than NO3- greater than I- greater than cyclamate- greater than SCN-) in both preparations. Twenty mmol/liter oxalate enhanced 45Ca2+ uptake in permeabilized cells 10-fold and in vesicles of endoplasmic reticulum, fivefold. Calcium oxalate precipitates in the endoplasmic reticulum of both preparations could be demonstrated by electron microscopy. The nonmitochondrial Ca2+ pool in permeabilized cells characterized in this study has been previously shown to regulate the cytosolic free Ca2+ concentration to 0.4 mumol/liter. Our results provide firm evidence that the endoplasmic reticulum plays an important role in the regulation of the cytosolic free Ca2+ concentration in pancreatic acinar cells.

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Section: Calcium-precipitating Anionsmentioning

confidence: 99%

Section: Monoualent Cationsmentioning

confidence: 99%

Characterization of calcium uptake into rough endoplamic reticulum of rat pancreas

et al. 1984

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“…1 demonstrate an apparent insensitivity of the Ca2 -ATPase toward exogenous Mg2+. Indeed, we [5] and others [3,4] have found that high concentrations of exogenous Mg2 + (required for Ca2 ' uptake) interfere with the detection of Ca2+-ATPase activity. This is due to the high basal Mg'+-ATPase activity present in the microsomal fraction [l -5, 26, 281.…”

Section: Discussionmentioning

confidence: 99%

The effect of Mg2+ on hepatic microsomal Ca2+ and Sr2+ transport

Fleschner¹,

Kraus‐Friedmann²

1986

Eur J Biochem

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The ATP-dependent uptake of Ca2+ by rat liver microsomal fraction is dependent upon Mg2'. Studies of the Mg2+ requirement of the underlying microsomal Ca2+-ATPase have been hampered by the presence of a large basal Mg2+-ATPase activity. We have examined the effect of various Mg2+ concentrations on Mg2 +-ATPase activity, Ca2+ uptake, Ca2+-ATPase activity and microsomal phosphoprotein formation.Both Mg2 In order to examine the apparent paradox of Mg2+ stimulation of Ca2+ uptake but not of Ca2+-ATPase activity, we examined the formation of the Ca2 +-ATPase phosphoenzyme intermediate and formation of a Mg2+-dependent phosphoprotein, which we have proposed to be an attribute of the Mg2+-ATPase activity. We found that Ca2+ apparently inhibited formation of the Mg2+-dependent phosphoprotein both in the absence and presence of exogenous Mg2 +. This suggests that Ca2+ may inhibit (at least partially) the Mg2+-ATPase activity.However, inclusion of the Ca2 + inhibition of Mg2 +-ATPase activity in the calculation of Ca2 +-ATPase activity reveals that this effect is insufficient to totally account for the stimulation of Ca2+ uptake by Mg2+. This suggests that Mg2+, in addition to stimulation of Ca2+-ATPase activity, may have a direct stimulatory effect on Ca2+ uptake in an as yet undefined fashion.In an effort to further examine the effect of Mg2+ on the microsomal Ca2+ transport system of rat liver, the interaction of this system with Sr2+ was examined. Sr2+ was sequestered into an A23187-releasable space in an ATP-dependent manner by rat liver microsomal fraction. The uptake of Sr2+ was similar to that of Ca2+ in terms of both rate and extent. A Sr2+-dependent ATPase activity was associated with the Sr2+ uptake. Sr2+ promoted formation of a phosphoprotein which was hydroxylamine-labile and base-labile. This phosphoprotein was indistinguishable from the Ca2 + -dependent ATPase phosphoenzyme intermediate. Sr2+ uptake was markedly stimulated by exogenous Mg2+, but the Sr2+-dependent ATPase activity was unaffected by increasing Mg2+ concentrations. Sr2+ uptake and %-'+-dependent ATPase activity were concomitantly inhibited by sodium vanadate.In contrast to Ca2+, Sr2+ had no effect on Mg2+-dependent phosphoprotein formation. Taken together, these data indicate that Mg2+ stimulated Ca2+ and Sr2+ transport by increasing the Ca2+(Sr2+)/ATP ratio. However, in the case of Ca2+ at least, these data must be interpreted with caution since Ca2+ may inhibit the Mg2+-ATPase activity.The ATP-dependent accumulation of Ca2+ by the rat liver microsomal fraction is now well documented. It is generally accepted that the enzymatic basis for the ATP-dependent Ca2 + accumulation is the microsomal Ca2 + -ATPase. Initially studies of this enzyme were hindered by the use of 5 mM

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“…Sodium/calcium countertransport is reported to be inhibited by glucose (Herchuelz, Sener & Malaisse, 1980). The calcium-ATPase is ATP dependent, as is calcium uptake into mitochondria (Sugden & Ashcroft, 1978) and endoplasmic reticulum (Colca et al 1982). So, increasing glucose could increase calcium buffering by any of these ATP-dependent processes.…”

Section: Intracellular Calcium Handlingmentioning

confidence: 99%

“…The steady reduction in intracellular calcium over the recovery period could be due to several cell processes: extrusion from the cell by the cell membrane calcium pump demonstrated in ,-cells (Pershadsingh, McDaniel, Landt, Bry, Lacy & McDonald, 1980); an increase in the sodium/calcium exchange that exists in f8-cells (Herchuelz, Sener & Malaisse, 1980) due to restoration of the sodium gradient and the rise in intracellular calcium; and/or uptake into cell organelles such as mitochondria (Sugden & Ashcroft, 1978), endoplasmic reticulum (Colca, McDonald, Kotagal, Patke, Fink, Greider, Lacy & McDaniel, 1982) and secretory granules (Abrahamsson, Gylfe & Hellman, 1981).…”

Section: Intracellular Calcium Handlingmentioning

confidence: 99%

The RESPONSE OF PANCREATIC Β‐CELL MEMBRANE POTENTIAL TO POTASSIUM‐INDUCED CALCIUM INFLUX IN THE PRESENCE OF GLUCOSE

1984

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SUMMARYMembrane potential measurements were made in pancreatic f-cells from microdissected islets from normal mice. In the presence of 11 mm glucose, depolarization of the membrane for 1 min with 50 mm potassium is followed by an inhibition of electrical activity before the normal burst pattern resumes. This inhibitory period, called the recovery time, is steady for each f-cell after three consecutive pulses of 50 mm potassium. The mean recovery time is 109 s. During the recovery time, the membrane is hyperpolarized and the input resistance is decreased, indicating that potassium permeability is high over this period. The recovery time is dependent on the size of the depolarization: 1 min exposure to potassium concentrations below 50 mm reduces the recovery time with a half-maximal effect at 38-5 mm potassium, corresponding to -27 mV. Also, increasing the extracellular calcium concentration lengthens the recovery time. Increasing the glucose concentration, however, shortens the recovery time. It is postulated that the recovery time represents activation of the calcium-gated potassium permeability and is a reflexion of the time taken for the fl-cell to buffer the increased intracellular calcium resulting from the potassium depolarization.

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Modulation of active Ca2+ uptake by the islet-cell endoplasmic reticulum

Cited by 27 publications

References 50 publications

Characterization of calcium uptake into rough endoplamic reticulum of rat pancreas

Characterization of calcium uptake into rough endoplamic reticulum of rat pancreas

The effect of Mg2+ on hepatic microsomal Ca2+ and Sr2+ transport

The RESPONSE OF PANCREATIC Β‐CELL MEMBRANE POTENTIAL TO POTASSIUM‐INDUCED CALCIUM INFLUX IN THE PRESENCE OF GLUCOSE

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