ISSN:
1432-2013
Keywords:
Key words Calcium channels
;
Human
;
Modulation
Source:
Springer Online Journal Archives 1860-2000
Topics:
Medicine
Notes:
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.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/s004240050691
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