Intracellular Ca2+pools in PC12 cells. A unique, rapidly exchanging pool is sensitive to both inositol 1,4,5-trisphosphate and caffeine-ryanodine (original) (raw)
Related papers
Biochemical Journal, 1991
In single bovine adrenal chromaffin cells loaded with fura-2, histamine, angiotensin II (AII) and caffeine elicited large transient increases of intracellular free Ca2+ concentration [( Ca2+]i) in the absence of external Ca2+, with peak amplitudes averaging 726 +/- 138 (n = 14), 710 +/- 102 (n = 21) and 830 +/- 100 nM (n = 30) respectively. A substantial portion of the agonist-induced rise in [Ca2+]i depended on Ca2+ release from caffeine-sensitive stores, as pretreatment with caffeine diminished subsequent agonist responses by 90-95%. Conversely, pretreatment with histamine or AII decreased subsequent caffeine responses by 100% and 90% respectively. The effects of caffeine most likely resulted from activation of a Ca(2+)-induced Ca(2+)-release (CICR) process, whereas histamine and AII initially acted through generation of Ins(1,4,5)P3. The relationship of Ins(1,4,5)P3- and caffeine-sensitive Ca2+ pools was studied by using alpha-toxin-permeabilized chromaffin cells. Evidence was fo...
Journal of Neurochemistry, 1990
Abstract: The effects of electrical stimulation, muscarinic and serotonergic agonists, and caffeine on [3H]inositol 1,4,5-trisphosphate ([3H]Ins(1,4,5)P3) content, intracellular free Ca2+ concentration ([Ca2+]i), and release of [3H]norepinephrine ([3H]NE) were studied in cultured sympathetic neurons. Neuronal cell body [Ca2+]i was unaffected by muscarinic or serotonergic receptor stimulation, which significantly increased [3H]Ins(1,4,5)P3 content. Stimulation at 2 Hz and caffeine had no effect on [3H]Ins(1,4,5)P3, but caused greater than two-fold increase in [Ca2+]i. Only 2-Hz stimulation released [3H]NE. Caffeine had no effect on the release. When [Ca2+]i was measured in growth cones, only electrical stimulation produced an increase in [Ca2+]i. The other agents had no effect on Ca2+ at the terminal regions of the neurons. We conclude that Ins(1,4,5)P3-insensitive, but caffeine-sensitive Ca2+ stores in sympathetic neurons are located only in the cell body and are not coupled to [3H]NE release.
Biochemical Journal, 1992
Ins(1,4,5)P3(InsP3)-induced Ca2+ release and [3H]InsP3 binding were measured in rat cerebellar microsomes in the presence or absence of caffeine. The quantal Ca2+ release was shown to occur in an apparently co-operative fashion with a Hill coefficient (h) of 2.2. Half-maximal Ca2+ release was observed at 900 nM-InsP3. Addition of caffeine caused changes both to the concentration of InsP3 required to cause half-maximal Ca2+ release (3.9 microM at 50 mM-caffeine) and to the apparent co-operativity (h = 1.0 at 50 mM-caffeine). Under standard conditions for [3H]InsP3 binding, caffeine had no effect, and it had no effect on InsP3 metabolism. Cyclic AMP also had no effect on the quantal release induced by InsP3. These results are consistent with the view that caffeine affects the opening (Ca2+ release) events rather than the ligand-binding events in the operation of the InsP3-sensitive Ca2+ channel.
The Journal of Membrane Biology, 1992
The effects of agents known to interfere with Ca 2+ release processes of endoplasmic reticulum were investigated in bradykinin (BK)-stimulated bovine aortic endothelial ceils (BAE cells), via the activation of Ca2+-activated potassium channels [K(Ca 2 § channels]. In cell-attached patch experiments, the external application of caffeine (1 mM) caused a brief activation of K(Ca 2+) channels in Ca2+-free and Ca2+-containing external solutions. The application of BK (10 riM) during cell stimulation by caffeine (1-20 mM) invariably led to a drastic channel activation which was maintained during a recording period longer than that observed in caffeine-free conditions. In addition, the cell exposure to caffeine (20 raM) during the BK stimulation enhanced systematically the channel activation process. Since a rapid inhibition of BK-evoked channel activity was also produced by removing caffeine from the bath medium, it is proposed that the sustained single-channel response recorded in the concomittant presence of both agents was due to their synergic action on internal stores and/or the external Ca 2+ entry pathway resulting in an increased [Ca2+] i. In addition, the local anesthetic, procaine, depressed the initial BK-induced K(Ca 2+) channel activity and completely blocked the secondary phase of the channel activation process related to the external Ca 2+ influx into stimulated cells. In contrast, this blocking effect of procaine was not observed on the initial caffeine-elicited channel activity and could not suppress the external Ca 2 +-dependent phase of this channel activation process. Our results confirm the existence of at least two pharmacologically distinct types of Ca2+-release from internal stores in BAE cells: an inositol 1,4,5-triphosphate (InsP3)-dependent and a caffeine-induced Ca2+-release process.
Pflugers Archiv-european Journal of Physiology, 1996
Caffeine, a well known facilitator of Ca2+-induced Ca2+ release, induced oscillations of cytosolic free Ca2+ ([Ca2+]i) in GH3 pituitary cells. These oscillations were dependent on the presence of extracellular Ca2+ and blocked by dihydropyridines, suggesting that they are due to Ca2+ entry through L-type Ca2+ channels, rather than to Ca2+ release from the intracellular Ca2+ stores. Emptying the stores by treatment with ionomycin or thapsigargin did not prevent the caffeine-induced [Ca2+]i oscillations. Treatment with caffeine occluded phase 2 ([Ca2+]i oscillations) of the action of thyrotropin-releasing hormone (TRH) without modifying phase 1 (Ca2+ release from the intracellular stores). Caffeine also inhibited the [Ca2+]i increase induced by depolarization with high-K+ solutions (56% at 20 mM), suggesting direct inhibition of the Ca2+ entry through voltage-gated Ca2+ channels. We propose that the [Ca2+]i increase induced by caffeine in GH3 cells takes place by a mechanism similar to that of TRH, i.e. membrane depolarization that increases the firing frequency of action potentials. The increase of the electrical activity overcomes the direct inhibitory effect on voltage-gated Ca2+ channels with the result of increased Ca2+ entry and a rise in [Ca2+]i. Consideration of this action cautions interpretation of previous experiments in which caffeine was assumed to increase [Ca2+]i only by facilitating the release of Ca2+ from intracellular Ca2+ stores.
Neuroscience, 1996
Abstraet--Cytosolic free calcium concentration ([Ca2+]c) was recorded from acutely isolated mouse dorsal root ganglion neurons loaded with Ca2+-indicator indo-1. The initiation of intracellular Ca 2÷ release by low (1-5 mM) caffeine concentrations failed to completely empty the caffeine-sensitive stores; subsequent challenge with higher doses of caffeine produced an additional [Ca2+]c elevation. This indicates a gradual Ca 2÷ release from caffeine-sensitive stores. The sensitivity of Ca 2÷ stores to caffeine was strongly influenced by endoplasmic reticulum luminal Ca 2+ concentration ([Ca2+]1) as an increase in [Ca2+Jj produced by a conditioning depolarization-induced Ca 2÷ entry, caused a several fold decrease of caffeine EC50.
Quantal Ca2+ release from caffeine-sensitive stores in adrenal chromaffin cells
The Journal of biological chemistry, 1993
In populations of fura-2-loaded chromaffin cells, caffeine caused a concentration-dependent increase in the intracellular Ca2+ concentration ([Ca2+]i), in the presence or absence of external Ca2+ ([Ca2+]o), that was saturable, reversible, and inhibited in a use-dependent fashion by ryanodine. These data confirm that caffeine mobilizes Ca2+ from the ryanodine-sensitive intracellular stores in chromaffin cells. In nominally Ca(2+)-free medium, sustained stimulation of cell populations or single cells with low caffeine concentrations failed to completely empty the caffeine-sensitive stores. In each case, there was a transient [Ca2+]i elevation, but a subsequent challenge with a higher caffeine concentration evoked a further [Ca2+]i rise, indicating that Ca2+ stores within individual cells were heterogeneous in their sensitivities to caffeine and that caffeine-induced Ca2+ release was quantal. The heterogeneous sensitivity was also demonstrated using ryanodine; pretreatment of cell popu...
Journal of General Physiology, 1994
A B S T R A C T Activation of ryanodine receptors on the sarcoplasmic reticulum of single smooth muscle cells from the stomach muscularis of Bufo marinus by caffeine is accompanied by a rise in cytoplasmic [Ca 2+] ([Ca2+]i), and the opening of nonselective cationic plasma membrane channels. To understand how each of these pathways contributes to the rise in [Ca2+]i, one needs to separately monitor Ca 2+ entry through them. Such information was obtained from simultaneous measurements of ionic currents and [Ca2+]i by the development of a novel and general method to assess the fraction of current induced by an agonist that is carried by Ca 2+. Application of this method to the currents induced in these smooth muscle cells by caffeine revealed that ~ 20% of the current passing through the membrane channels activated following caffeine application is carried by Ca 2+. Based on this information we found that while Ca 2 § entry through these channels rises slowly, release of Ca z+ from stores, while starting at the same time, is much faster and briefer. Detailed quantitative analysis of the Ca 2 § release from stores suggests that it most likely decays due to depletion of Ca 2+ in those stores. When caffeine was applied twice to a cell with only a brief (30 s) interval in between, the amount of Ca 2+ released from stores was markedly diminished following the second caffeine application whereas the current carried in part by Ca 2+ entry across the plasma membrane was not significantly affected. These and other studies described in the preceding paper indicate that activation of the nonselective cation plasma membrane channels in response to caffeine was not caused as a consequence of emptying of internal Ca 2+ stores. Rather, it is proposed that caffeine activates these membrane channels either by direct interaction or alternatively by a linkage between Pacaud, P., and T. B. Bolton. 1991. Relation between muscarinic receptor cationic current and internal calcium in guinea-pig jejunal smooth muscle cells.Journal of Physiology. 441:477-499. Pessah, I. N., R. A. Stambuk, and J. E. Casida. 1987. Ca2+-activated ryanodine binding: mechanisms of sensitivity and intensity modulation by Mg 2+, caffeine, and adenine nucleotides. Molecular
Caffeine-induced calcium release from internal stores in cultured rat sensory neurons
Neuroscience, 1993
Free intracellular calcium concentration ([&"I,,) was recorded at 22°C by means of Indo-l or Fura-single-cell microfluorometry in cultured dorsal root ganglion neurons obtained from neonatal rats. The resting [Ca2+li, in dorsal root ganglion neurons was 73 + 21 nM (mean f S.D., n = 94). Fast application of 20 mM caffeine evoked [Ca*+],, transient which reached a peak of 269 k 64 nM wlthin 5.9 + 1.1 s. After reaching the peak the [Ca*+],, level started to decline in the presence of caffeine and for 87.2 + 10.6 s cytoplasmic calcium returned to an initial resting value. In 40% of neurons tested [Ca*+]," decreased to subresting levels following the washout of caffeine (the so-called post-caffeine undershoot). On average, the undershoot level was 19 &-2.5 nM below the resting [Ca*+],, value. Prolonged exposure of caffeine depleted the caffeine-sensitive stores of releasable Ca 2+; the degree of this depletion depended on caffeine concentration. The depletion of the caffeine-sensitive internal stores to some extent was linked to calcium extrusion via La'+-sensitive plasmalemmal Ca '+-ATPases. The stores could be partially refilled bv the uptake of cytoplasmic Ca 2+, but the complete recovery of releasable Ca*+ content of the
Different properties of caffeine-sensitive Ca 2+ stores in peripheral and central mammalian neurones
Pflugers Archiv-european Journal of Physiology, 1994
Using indo-1 based microfluorometry for measuring the cytoplasmic free calcium concentration ([Ca2+]i), the properties of caffeine-induced Ca2+ release from internal stores were studied in rat cultured central and peripheral neurones, including dorsal root ganglia (DRG) neurones, neurones from nucleus cuneatus, CA1 and CA3 hippocampal region and pyramidal neocortical neurones. Under resting conditions the Ca2+ content of internal stores in DRG neurones was high enough to produce caffeine-triggered [Ca2+]i transients. Caffeine-induced Ca2+ release depleted internal stores in DRG neurones, but they refilled themselves spontaneously up to 81.4±5.67 % within 10 minutes. In contrast, in all types of central neurones the resting Ca2+ content of internal stores was low, but the stores could be charged by transmembrane Ca2+ influx through voltage-operated calcium channels. After charging, the stores in central neurones spontaneously lost releasable calcium content and within 10 minutes they emptied again. We suggest that in sensory neurones calcium stores are continuously filled by releasable calcium and after discharge they can refill themselves spontaneously, while in central neurones internal calcium stores can be charged by releasable calcium only transiently.