Different types of calcium channels and secretion from bovine chromaffin cells

Abstract

Bovine chromaffin cells possess several types of Ca2+ channels, and influx of Ca2+ is known to trigger secretion. However, discrepant information about the relative importance of the individual subtypes in secretion has been reported. We used whole-cell patch-clamp measurements in isolated cells in culture combined with fura-2 microfluorimetry and pharmacological manipulation to determine the dependence of secretion on different types of Ca2+ channels. We stimulated cells with relatively long depolarizing voltage-clamp pulses in a medium containing 60 mM CaCl2. We found that, within a certain range of pulse parameters, secretion as measured by membrane capacitance changes was mainly determined by the total cumulative charge of Ca2+ inflow and the basal [Ca2+] level preceding a stimulus. Blocking or reducing the contribution of specific types of Ca2+ channels using either 20 microM nifedipine plus 10 microM nimodipine or 1 microM omegaCTxGVIA (omega-conotoxin GVIA) or 2 microM omegaCTxMVIIC (omega-conotoxin MVIIC) reduced secretion in proportion to Ca2+ charge, irrespective of the toxin used. We conclude that for long-duration stimuli, which release a large fraction of the readily releasable pool of vesicles, it is not so important through which type of channels Ca2+ enters the cell. Release is determined by the total amount of Ca2+ entering and by the filling state of the readily releasable pool, which depends on basal [Ca2+] before the stimulus. This result does not preclude that other stimulation patterns may lead to responses in which subtype specificity of Ca2+ channels matters.

Overexpression of an α1H (Cav3.2) T-type Calcium Channel during Neuroendocrine Differentiation of Human Prostate Cancer Cells

“…Indeed, it was shown that secretion of mitogenic peptides by LNCaP cells is enhanced during neuroendocrine differentiation (5). Furthermore, it is known that calcium is the main ion involved in the control of exocytosis in many cell models and a fundamental role has been shown for L-type and N-and P/Q-type calcium channels in neuroendocrine cells (43). Few studies have demonstrated a direct role of T-type calcium channels in exocytosis (44).…”

CaV1.3 as pacemaker channels in adrenal chromaffin cells: Specific role on exo- and endocytosis?

“…[12][13][14][15] In rat (RCCs) and mouse chromaffin cells (MCCs) they are responsible for nearly half of the total Ca 2+ current and the corresponding exocytosis. 12,[16][17][18][19][20] Second, compensatory and excess endocytosis are strongly attenuated when LTCCs are blocked. 21 Third, LTCC gating can be either up or downregulated by autocrinally released neurotransmitters coupled to membrane-delimited G protein dependent receptors or cGMP/PKG and cAMP/PKA pathways.…”

“…12,[17][18][19][64][65][66][67][68] Secretion is not particularly linked to a specific Ca 2+ channel type and either deletion or upregulation of one of them causes a proportional change to secretion. For instance, Ca V 2.1 deletion causes a loss of the P/Q-type currents with a compensatory increase of L-type currents and secretion.…”

Fast exocytosis mediated by T- and L-type channels in chromaffin cells: distinct voltage-dependence but similar Ca2+-dependence

“…This slower exocytotic process is primarily controlled by Ca 2+ inXux through multiple isoforms of high-voltage activated Ca 2+ channels, which contribute to secretion proportionally to their density of expression and gating properties, with no speciWc requirements of Ca 2+ channels colocalization to the release sites (Kim et al 1995;Engisch and Nowycky 1996;Klingauf and Neher 1997;Lukyanetz and Neher 1999;Ulate et al 2000;Carabelli et al 2003;Chan et al 2005;Giancippoli et al 2006;Polo-Parada et al 2006). Alternatively, other groups suggest a preferential role of some channel subtype in close proximity to the secretory sites (Lopez et al 1994;Artalejo et al 1994;Lara et al 1998;O'Farrel and Marley 2000;Albillos et al 2000) and a further role of mitochondria in sequestering Ca 2+ entering through Ca 2+ channels (Ales et al 2005).…”