HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Villarroya, M. Articles by García, A. G. Search for Related Content PubMed PubMed Citation Articles by Villarroya, M. Articles by García, A. G.

Voltage inactivation of Ca²⁺ entry and secretion associated with N- and P/Q-type but not L-type Ca²⁺ channels of bovine chromaffin cells

Mercedes Villarroya *, Román Olivares *, Ana Ruíz *, María F. Cano-Abad *, Ricardo de Pascual *, Richard B. Lomax *, Manuela G. López *, Inés Mayorgas *, Luis Gandía * and Antonio G. García *¹

In this study we pose the question of why the bovine adrenal medullary chromaffin cell needs various subtypes (L, N, P, Q) of the neuronal high-voltage activated Ca²⁺ channels to control a given physiological function, i.e. the exocytotic release of catecholamines. One plausible hypothesis is that Ca²⁺ channel subtypes undergo different patterns of inactivation during cell depolarization.

The net Ca²⁺ uptake (measured using ⁴⁵Ca²⁺) into hyperpolarized cells (bathed in a nominally Ca²⁺-free solution containing 1·2 mM K⁺) after application of a Ca²⁺ pulse (5 s exposure to 100 mM K⁺ and 2 mM Ca²⁺), amounted to 0·65 ± 0·02 fmol cell^-1; in depolarized cells (bathed in nominally Ca²⁺-free solution containing 100 mM K⁺) the net Ca²⁺ uptake was 0·16 ± 0·01 fmol cell^-1.

This was paralleled by a dramatic reduction of the increase in the cytosolic Ca²⁺ concentration, [Ca²⁺]_i, caused by Ca²⁺ pulses applied to fura-2-loaded single cells, from 1181 ± 104 nM in hyperpolarized cells to 115 ± 9 nM in depolarized cells.

A similar decrease was observed when studying catecholamine release. Secretion was decreased when K⁺ concentration was increased from 1·2 to 100 mM; the Ca²⁺ pulse caused, when comparing the extreme conditions, the secretion of 807 ± 35 nA of catecholamines in hyperpolarized cells and 220 ± 19 nA in depolarized cells.

The inactivation by depolarization of Ca²⁺ entry and secretion occluded the blocking effects of combined -conotoxin GVIA (1 µM) and -agatoxin IVA (2 µM), thus suggesting that depolarization caused a selective inactivation of the N- and P/Q-type Ca²⁺ channels.

This was strengthened by two additional findings: (i) nifedipine (3 µM), an L-type Ca²⁺ channel blocker, suppressed the fraction of Ca²⁺ entry (24 %) and secretion (27 %) left unblocked by depolarization; (ii) FPL64176 (3 µM), an L-type Ca²⁺ channel 'activator', dramatically enhanced the entry of Ca²⁺ and the secretory response in depolarized cells.

In voltage-clamped cells, switching the holding potential from -80 to -40 mV promoted the loss of 80 % of the whole-cell inward Ca²⁺ channel current carried by 10 mM Ba²⁺ (I_Ba). The residual current was blocked by 80 % upon addition of 3 µM nifedipine and dramatically enhanced by 3 µM FPL64176.

Thus, it seems that the N- and P/Q-subtypes of calcium channels are more prone to inactivation at depolarizing voltages than the L-subtype. We propose that this different inactivation might occur physiologically during different patterns of action potential firing, triggered by endogenously released acetylcholine under various stressful conditions.

This article has been cited by other articles:

				A. G. Garcia, A. M. Garcia-De-Diego, L. Gandia, R. Borges, and J. Garcia-Sancho Calcium signaling and exocytosis in adrenal chromaffin cells. Physiol Rev, October 1, 2006; 86(4): 1093 - 1131. [Abstract] [Full Text] [PDF]

				E. V. Dzhura, W. He, and K. P. M. Currie Linopirdine Modulates Calcium Signaling and Stimulus-Secretion Coupling in Adrenal Chromaffin Cells by Targeting M-Type K+ Channels and Nicotinic Acetylcholine Receptors J. Pharmacol. Exp. Ther., March 1, 2006; 316(3): 1165 - 1174. [Abstract] [Full Text] [PDF]

				A. Giancippoli, M. Novara, A. de Luca, P. Baldelli, A. Marcantoni, E. Carbone, and V. Carabelli Low-Threshold Exocytosis Induced by cAMP-Recruited CaV3.2 ({alpha}1H) Channels in Rat Chromaffin Cells Biophys. J., March 1, 2006; 90(5): 1830 - 1841. [Abstract] [Full Text] [PDF]

				A. I. Cowan and C. Stricker Functional Connectivity in Layer IV Local Excitatory Circuits of Rat Somatosensory Cortex J Neurophysiol, October 1, 2004; 92(4): 2137 - 2150. [Abstract] [Full Text] [PDF]

				M. Shiraishi, I. Shibuya, K. Minami, Y. Uezono, T. Okamoto, N. Yanagihara, S. Ueno, Y. Ueta, and A. Shigematsu A Neurosteroid Anesthetic, Alphaxalone, Inhibits Nicotinic Acetylcholine Receptors in Cultured Bovine Adrenal Chromaffin Cells Anesth. Analg., October 1, 2002; 95(4): 900 - 906. [Abstract] [Full Text] [PDF]

				M. F. Cano-Abad, M. Villarroya, A. G. Garcia, N. H. Gabilan, and M. G. Lopez Calcium Entry through L-type Calcium Channels Causes Mitochondrial Disruption and Chromaffin Cell Death J. Biol. Chem., October 19, 2001; 276(43): 39695 - 39704. [Abstract] [Full Text] [PDF]

				T. Nagayama, Y. Fukushima, H. Hikichi, M. Yoshida, M. Suzuki-Kusaba, H. Hisa, T. Kimura, and S. Satoh Interaction of SKCa channels and L-type Ca2+ channels in catecholamine secretion in the rat adrenal gland Am J Physiol Regulatory Integrative Comp Physiol, November 1, 2000; 279(5): R1731 - R1736. [Abstract] [Full Text] [PDF]