Inhibition of N and PQ calcium channels by calcium entry through L channels in chromaffin cells

Rosa, Juliana M.; Gandı́a, Luis; Garcı́a, Antonio G.

doi:10.1007/s00424-009-0662-2

Cited by 12 publications

(10 citation statements)

References 73 publications

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“…Nonetheless, both BayK and FPL, similar to other cells that express L-type channels, augment Ca 2ϩ influx in bovine chromaffin cells as reported previously (26,28,29,54,55).…”

Section: Bayk Accelerated the Frequency Of Catecholamine Secretion Inmentioning

confidence: 54%

Conformational Changes Induced in Voltage-gated Calcium Channel Cav1.2 by BayK 8644 or FPL64176 Modify the Kinetics of Secretion Independently of Ca2+ Influx

Marom

Hagalili

Sebag

et al. 2010

Journal of Biological Chemistry

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The role of the L-type calcium channel (Cav1.2) as a molecular switch that triggers secretion prior to Ca 2؉ transport has previously been demonstrated in bovine chromaffin cells and rat pancreatic beta cells. Here, we examined the effect of specific Cav1.2 allosteric modulators, BayK 8644 (BayK) and FPL64176 (FPL), on the kinetics of catecholamine release, as monitored by amperometry in single bovine chromaffin cells. We show that 2 M BayK or 0.5 M FPL accelerates the rate of catecholamine secretion to a similar extent in the presence either of the permeable Ca 2؉ and Ba 2؉ or the impermeable charge carrier La 3؉ . These results suggest that structural rearrangements generated through the binding of BayK or FPL, by altering the channel activity, could affect depolarization-evoked secretion prior to cation transport. FPL also accelerated the rate of secretion mediated by a Ca 2؉ -impermeable channel made by replacing the wild type ␣ 1 1.2 subunit was replaced with the mutant ␣ 1 1.2/ L775P. Furthermore, BayK and FPL modified the kinetic parameters of the fusion pore formation, which represent the initial contact between the vesicle lumen and the extracellular medium. A direct link between the channel activity and evoked secretion lends additional support to the view that the voltagegated Ca 2؉ channels act as a signaling molecular switch, triggering secretion upstream to ion transport into the cell.The kinetic properties of voltage-gated Ca 2ϩ channels (VGCC) 2 are determined by the conformational changes induced at the channel during membrane depolarization. The kinetics of the L-type VGCC Cav1 is modulated also by allosteric agonists, which include BayK 8644 (BayK), a 1,4-dihydropyridine, FPL64176 (FPL), and CGP 48506 (1-9). BayK, FPL, and CGP 48506, which are structurally unrelated, interact with the cardiac Cav1.2 channel through binding within discrete sites at the transmembrane and extracellular loops of the ␣ 1 1.2 pore-forming subunit (10 -14). BayK enhances macroscopic currents (15) by increasing the rate of transition to "mode 2" single channel behavior (16,17) and the single channel currents by means of lengthening the channel open time (17)(18)(19)(20). BayK binding at selective Cav1.2 regions alters indirectly the selectivity filter, in turn affecting ion permeability (21). The changes observed in channel deactivation and inactivation are sensitive to the type of the cation used as the charge carrier (17).Like BayK 8644 (1), FPL is coupled to the cation binding at the selectivity filter of Cav1.1 acting as an allosteric regulator (22). In neonatal rat ventricular myocytes and rat ventricular cells, FPL enhances Ca 2ϩ influx and slows both the activation and the inactivation kinetics of the Cav1.2 (23). In isolated rat ventricular myocytes, FPL slowed the transition of the channel to a closed or inactivated state (24). In GH3 cells, FPL increased Cav1.2 current amplitude and shifted the current-voltage relationship to negative voltages (25). Single channel analysis showed that FPL increased both the...

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“…Nonetheless, both BayK and FPL, similar to other cells that express L-type channels, augment Ca 2ϩ influx in bovine chromaffin cells as reported previously (26,28,29,54,55).…”

Section: Bayk Accelerated the Frequency Of Catecholamine Secretion Inmentioning

confidence: 54%

Conformational Changes Induced in Voltage-gated Calcium Channel Cav1.2 by BayK 8644 or FPL64176 Modify the Kinetics of Secretion Independently of Ca2+ Influx

Marom

Hagalili

Sebag

et al. 2010

Journal of Biological Chemistry

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“…Greater reduction of Q Ca was likely due to higher Ca 2ϩ -dependent inactivation of N and PQ channels (33,58). This led to a 22% reduction of ⌬C m and to as much as 93% reduction of C m decay ( Fig.…”

Section: Resultsmentioning

confidence: 94%

“…Cell loading with EGTA was performed to prevent Ca 2ϩ -dependent inactivation of VDCCs by excessive intracellular Ca 2ϩ ([Ca 2ϩ ]c) rise (58).…”

Section: Methodsmentioning

confidence: 99%

Calcium entry through slow-inactivating L-type calcium channels preferentially triggers endocytosis rather than exocytosis in bovine chromaffin cells

Rosa¹,

Torregrosa‐Hetland

Colmena³

et al. 2011

American Journal of Physiology-Cell Physiology

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Calcium (Ca(2+))-dependent endocytosis has been linked to preferential Ca(2+) entry through the L-type (α(1D), Ca(V)1.3) of voltage-dependent Ca(2+) channels (VDCCs). Considering that the Ca(2+)-dependent exocytotic release of neurotransmitters is mostly triggered by Ca(2+) entry through N-(α(1B), Ca(V)2.2) or PQ-VDCCs (α(1A), Ca(V)2.1) and that exocytosis and endocytosis are coupled, the supposition that the different channel subtypes are specialized to control different cell functions is attractive. Here we have explored this hypothesis in primary cultures of bovine adrenal chromaffin cells where PQ channels account for 50% of Ca(2+) current (I(Ca)), 30% for N channels, and 20% for L channels. We used patch-clamp and fluorescence techniques to measure the exo-endocytotic responses triggered by long depolarizing stimuli, in 1, 2, or 10 mM concentrations of extracellular Ca(2+) ([Ca(2+)](e)). Exo-endocytotic responses were little affected by ω-conotoxin GVIA (N channel blocker), whereas ω-agatoxin IVA (PQ channel blocker) caused 80% blockade of exocytosis as well as endocytosis. In contrast, nifedipine (L channel blocker) only caused 20% inhibition of exocytosis but as much as 90% inhibition of endocytosis. Conversely, FPL67146 (an activator of L VDCCs) notably augmented endocytosis. Photoreleased caged Ca(2+) caused substantially smaller endocytotic responses compared with those produced by K(+) depolarization. Using fluorescence antibodies, no colocalization between L, N, or PQ channels with clathrin was found; a 20-30% colocalization was found between dynamin and all three channel antibodies. This is incompatible with the view that L channels are coupled to the endocytotic machine. Data rather support a mechanism implying the different inactivation rates of L (slow-inactivating) and N/PQ channels (fast-inactivating). Thus a slow but more sustained Ca(2+) entry through L channels could be a requirement to trigger endocytosis efficiently, at least in bovine chromaffin cells.

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“…For example, Ca 2+ entry through L-type VOCCs favoured the inhibition of N and P/Q channels in voltage-clamped bovine adrenal chromaffin cells (Rosa et al, 2009). Therefore, when a nicotinic agonist acts on non-a7 nAChRs, coupled to L-type Ca 2+ channels, the a7 nAChRs are inactivated because they are coupled to non-L Ca 2+ channels that inactivate more rapidly (Villarroya et al, 1999).…”

Section: Substitution Of Namentioning

confidence: 99%

Calcium signalling mediated through α7 and non‐α7 nAChR stimulation is differentially regulated in bovine chromaffin cells to induce catecholamine release

Barrio

Egea

León

et al. 2010

British J Pharmacology

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BACKGROUND AND PURPOSE Ca2+ signalling and exocytosis mediated by nicotinic receptor (nAChR) subtypes, especially the a7 nAChR, in bovine chromaffin cells are still matters of debate. EXPERIMENTAL APPROACHWe have used chromaffin cell cultures loaded with Fluo-4 or transfected with aequorins directed to the cytosol or mitochondria, several nAChR agonists (nicotine, 5-iodo-A-85380, PNU282987 and choline), and the a7 nAChR allosteric modulator PNU120596. KEY RESULTS Minimal [Ca 2+]c transients, induced by low concentrations of selective a7 nAChR agonists and nicotine, were markedly increased by the a7 nAChR allosteric modulator PNU120596. These potentiated responses were completely blocked by the a7 nAChR antagonist a-bungarotoxin (a7-modulated-response). Conversely, high concentrations of the a7 nAChR agonists, nicotine or 5-iodo-A-85380 induced larger [Ca 2+ ]c transients, that were blocked by mecamylamine but were unaffected by a-bungarotoxin (non-a7 response). [Ca 2+ ]c increases mediated by a7 nAChR were related to Ca 2+ entry through non-L-type Ca 2+ channels, whereas non-a7 nAChR-mediated signals were related to L-type Ca 2+ channels; Ca [Ca 2+ ]c and catecholamine release mediated by a7 nAChRs required an allosteric modulator and low doses of the agonist. At higher agonist concentrations, the a7 nAChR response was lost and the non-a7 nAChRs were activated. Catecholamine release might therefore be regulated by different nAChR subtypes, depending on agonist concentrations and the presence of allosteric modulators of a7 nAChRs. [Ca 2+ ]c, cytosolic concentration of calcium; BGT, a-bungarotoxin; DMEM, Dulbecco's modified Eagle's medium; ER, endoplasmic reticulum; nAChR, nicotinic acetylcholine receptor; VOCC, voltage operated calcium channel BJP British Journal of Pharmacology CONCLUSIONS AND IMPLICATIONS Abbreviations

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Inhibition of N and PQ calcium channels by calcium entry through L channels in chromaffin cells

Cited by 12 publications

References 73 publications

Conformational Changes Induced in Voltage-gated Calcium Channel Cav1.2 by BayK 8644 or FPL64176 Modify the Kinetics of Secretion Independently of Ca2+ Influx

Conformational Changes Induced in Voltage-gated Calcium Channel Cav1.2 by BayK 8644 or FPL64176 Modify the Kinetics of Secretion Independently of Ca2+ Influx

Calcium entry through slow-inactivating L-type calcium channels preferentially triggers endocytosis rather than exocytosis in bovine chromaffin cells

Calcium signalling mediated through α7 and non‐α7 nAChR stimulation is differentially regulated in bovine chromaffin cells to induce catecholamine release

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