Exposure of rat pheochromocytoma (PC12) cells to cyanide produces elevation of cytosolic calcium, impaired Na(+)-H+ exchange, membrane lipid peroxidation and release of neurotransmitters. Since these observations suggested cyanide alters plasma membrane function, the present study examined the effect of NaCN on the membrane potential of undifferentiated PC12 cells in suspension. In PC12 cells loaded with the voltage sensitive fluorescent dye, bis-oxonol, cyanide (2.5-10 mM) elicited an immediate (within seconds), concentration related decrease in fluorescence, indicating hyperpolarization of the plasma membrane. Increasing extracellular K+ concentration to 20 mM blocked the effect of cyanide (5 mM), suggesting cyanide increased K+ efflux. Pretreatment with quinine blocked the cyanide-induced hyperpolarization, whereas glyburide had little effect, showing the hyperpolarization produced by cyanide was due to activation of Ca2+ sensitive K+ channels. Removal of Ca2+ from the media did not influence cyanide-induced hyperpolarization. However, buffering intracellular Ca2+ by loading cells with the Ca2+ chelators, Quin II or BAPTA, abolished the cyanide effect, showing cytosolic Ca2+ is a key factor. These findings suggest that cyanide mobilizes Ca2+ from intracellular stores which leads to hyperpolarization via the activation of Ca2+ sensitive K+ channels.
"Fifth, there is a notable lack of evidence for the presence of K ATP channels in PC -12 cells; a detailed analysis of K ϩ channel types in these cells revealed the presence of four distinct K ϩ channel types, none of which were K ATP channels (Conforti and Millhorn, 1997). Furthermore, although cyanide causes hyperpolarization of PC-12 cells, this is unaffected by glibenclamide and is attributable instead to release of Ca 2ϩ from internal stores and a consequent activation of Ca 2ϩ -dependent K ϩ channels (Latha et al., 1994). "
[Show abstract][Hide abstract] ABSTRACT: Electrochemical detection of quantal catecholamine release from PC-12 cells revealed that glibenclamide, an inhibitor of ATP-sensitive K(+) channels, potentiated Ca(2+)-dependent exocytosis evoked by raised extracellular [K(+)] and by exposure of cells to caffeine. Glibenclamide was without effect on voltage-gated Ca(2+) currents, membrane potential, or rises of [Ca(2+)](i) evoked by either raised extracellular [K(+)] or caffeine. The dependence of K(+)-evoked secretion on extracellular Ca(2+) was shifted leftward in the presence of glibenclamide, with a small increase in the plateau level of release, suggesting that glibenclamide primarily increased the Ca(2+) sensitivity of the exocytotic apparatus. Enhancement of secretion by glibenclamide was reversed by pinacidil and cromakalim, indicating that the effects of glibenclamide were mediated via an action on a sulfonylurea receptor. These results demonstrate that sulfonylurea receptors can modulate Ca(2+)-dependent exocytosis via a mechanism downstream of Ca(2+) influx or mobilization.
The Journal of Neuroscience : The Official Journal of the Society for Neuroscience 08/1999; 19(14):5741-9. · 6.34 Impact Factor
"One must, therefore, consider some alternative hyperpolarizing mechanism. It is well known that CN raises cytoplasmic free Ca 2ϩ in a variety of cells—including several types of neurons (Biscoe and Duchen, 1990; Duchen et al., 1990; Dubinsky and Rothman, 1991; Duchen and Biscoe, 1992; Kaplin et al., 1996), as well as glia (Brismar and Collins, 1993), vascular smooth muscle (Miller et al., 1993), and chromaffin cells (Latha et al., 1994). CN thus could produce hyperpolarization by activating a Ca 2ϩ -sensitive G K (G K(Ca) ). "
[Show abstract][Hide abstract] ABSTRACT: The rapid suppression of CNS function produced by cyanide (CN) was studied by field, intracellular, and whole-cell recording in hippocampal slices (at 33-34 degrees C). Population spikes and field EPSPs were depressed by 4-5 min bath applications of 50-100 microM CN (IC50 was 18 miroM for spikes and 72 microM for EPSPs). The actions of CN were reversibly suppressed by the adenosine antagonists 8-sulfophenyltheophylline (8-SPT; 10 microM) and 8-cyclopentyl-1,3-dipropylxanthine (DPCPX; 0.2 microM), potentiated by the adenosine transport inhibitor dipyridamole (0.5 microM), but unaffected by the KATP channel blocker glyburide (10 microM). Therefore the CN-induced reductions of synaptic efficacy and postsynaptic excitability-demonstrated by synaptic input:output plots-are mediated mainly by adenosine. In whole-cell or intracellular recordings, CN depressed EPSCs and elicited an increase in input conductance and an outward current, the reversal potential of which was approximately -90 mV (indicating that K+ was the major carrier). These effects also were attenuated by 8-SPT. In the presence of 1 mM Ba, CN had no significant postsynaptic action; Cs (2 mM) also prevented CN-induced outward currents but only partly blocked the increase in conductance. Another 8-SPT-sensitive action of CN was to depress hyperpolarization-activated slow inward relaxations (Q current). At room temperature (22-24 degrees C), although it did not change holding current and slow inward relaxations, CN raised the input conductance; this effect also was prevented by 8-SPT (10 microM), but not by glyburide (10 microM). Adenosine release thus appears to be the major link between acute CN poisoning and early depression of CNS synaptic function.
The Journal of Neuroscience : The Official Journal of the Society for Neuroscience 05/1997; 17(7):2355-64. · 6.34 Impact Factor
"Ca'~'. influx may also contribute to hypoxia-induced increases in Ca'~'i, because placing cells in a Ca* ' -free solution resulted in a partial decrease in the levels of Ca2+i that were obtained (Krnjevic and Xu, 1989; Biscoe and Duchen, 1990; Duchcn et al., 1990; Hasham et al., 1994; Latha et al., 1994). Numerous examples exist in which mobilization of Ca' + from IP,-sensitive stores subsequently leads to Ca' ' influx (Irvine , 1992; Fasolato et al., 1994). "
[Show abstract][Hide abstract] ABSTRACT: To evaluate the relationship of inositol 1,4,5-trisphosphate (IP3) receptor-mediated signal transduction and cellular energy dynamics, we have characterized effects of nucleotides on IP3 receptor (IP3R)-mediated calcium (Ca2+) flux in purified IP3 receptors reconstituted in lipid vesicles (IP3RV) and examined hypoxia-induced augmentation of intracellular Ca2+ in intact cells. Reduced nicotinamide adenine dinucleotide (NADH) increases IP3-mediated Ca2+ flux in IP3RV. This effect is highly specific for NADH. Hypoxia elicited by brief exposure of nerve growth factor-differentiated PC12 cells or cerebellar Purkinje cells to cyanide elicits rapid increased in internal [Ca2+], which derives from IP3-sensitive stores. Blockade of this effect by 2-deoxyglucose and inhibition of glyceraldehyde-3-phosphate dehydrogenase implicates enhanced glycolytic production of NADH in the Ca2+ stimulation. Internal [Ca2+] is markedly and specifically increased by direct intracellular injection of NADH, and this effect is blocked by heparin, further implicating IP3R stores. These findings indicate that direct regulation of IP3R by NADH is responsible for elevated cytoplasmic [Ca2+] occurring in the earliest phase of hypoxia. This link of IP3R activity with cellular energy dynamics may be relevant to both hypoxic damage and metabolic regulation of IP3 signaling processes.
The Journal of Neuroscience : The Official Journal of the Society for Neuroscience 04/1996; 16(6):2002-11. · 6.34 Impact Factor
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