Human adrenal chromaffin cell calcium channels: drastic current facilitation in cell clusters, but not in isolated cells |
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Authors: | Luis Gandía Inés Mayorgas Pedro Michelena Inmaculada Cuchillo Ricardo de Pascual Francisco Abad Jesús M Novalbos Eduardo Larrañaga A G García |
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Institution: | (1) Instituto de Farmacología Teófilo Hernando, Departamento de Farmacología, Facultad de Medicina, Universidad Autónoma de Madrid, Arzobispo Morcillo, 4; E-28029 Madrid. Spain e-mail: agg@mvax.fmed.uam.es Tel.: +34-91-3975388, Fax: +34-91-3975397, ES;(2) Servicio de Farmacología Clínica e Instituto de Gerontología, Hospital de la Princesa, Diego de León, 62; E-28006 Madrid, Spain, ES;(3) Servicio de Cirugía, Hospital Universitario de la Princesa, Diego de León, 62; E-28006 Madrid, Spain, ES |
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Abstract: | Human adrenal medullary chromaffin cells were prepared and cultured from a cystic tumoral adrenal gland whose medullary tissue
was unaffected. Adrenaline-containing and noradrenaline-containing cells were identified using a confocal fluorescence microscope
and antibodies against dopamine beta-hydroxylase (DBH) and phenylethanolamine N-methyltransferase (PNMT). Current/voltage (I/V) curves performed with the voltage-clamped cells bathed in 10 mM Ba2+ (holding potential, V
h=–80 mV) revealed the presence of only high-threshold voltage-dependent Ca2+ channels; T-type Ca2+ channels were not seen. By using supramaximal concentrations of selective Ca2+ channel blockers, the whole-cell I
Ba could be fractionated into various subcomponents. Thus, I
Ba had a 25% fraction sensitive to 1 μM nifedipine (L-type channels), 21% sensitive to 1 μM ω-conotoxin GVIA (N-type channels),
and 60% sensitive to 2 μM ω-agatoxin IVA (P/Q-type channels). The activation of I
Ba was considerably slowed down, and the peak current was inhibited upon superfusion with 10 μM ATP. The slow activation and
peak current blockade were reversed by strong depolarizing pre-pulses to +100 mV (facilitation). A drastic facilitation of
I
Ba was also observed in voltage-clamped human chromaffin cell surrounded by other unclamped cells; in contrast, in voltage-clamped
cells not immersed in a cell cluster, facilitation was scarce. So, facilitation of Ca2+ channels in a voltage-clamped cell seems to depend upon the exocytotic activity of neighbouring unclamped cells, which is
markedly increased by Ba2+. It is concluded that human adrenal chromaffin cells mostly express P/Q-types of voltage-dependent Ca2+ channels (60%). L-Type channels and N-type channels are also expressed, but to a considerably minor extent (around 20% each).
This dominance of P/Q-type channels in human chromaffin cells clearly contrasts with the relative proportion of each channel
type expressed by chromaffin cells of five other animal species studied previously, where the P/Q-type channels accounted
for 5–50%. The results also provide strong support for the hypothesis that Ca2+ channels of human chromaffin cells are regulated in an autocrine/paracrine fashion by materials co-secreted with the catecholamines,
i.e. ATP and opiates.
Received: 1 May 1998 / Received after revision and accepted: 21 May 1998 |
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Keywords: | Calcium channels Human Modulation |
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