Premium
R56865 inhibits catecholamine release from bovine chromaffin cells by blocking calcium channels
Author(s) -
GarcezDoCarmo Lucía,
Albillos Almudena,
Artalejo Antonio R.,
Fuente MaríaTeresa,
López Manuela G.,
Gandía Luis,
Michelena Pedro,
García Antonio G.
Publication year - 1993
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/j.1476-5381.1993.tb13934.x
Subject(s) - catecholamine , secretion , chemistry , ic50 , chromaffin cell , biophysics , calcium , endocrinology , medicine , patch clamp , blockade , depolarization , fura 2 , adrenal medulla , cytosol , in vitro , biology , biochemistry , receptor , organic chemistry , enzyme
1 The effects of R56865 (a new class of cardioprotective agent which prevents Na + and Ca 2+ overload in cardiac myocytes) on catecholamine release, whole‐cell current through Ca 2+ channels ( I Ba ) and cytosolic Ca 2+ concentrations, [Ca 2+ ] i , have been studied in bovine chromaffin cells. 2 R56865 caused a time‐ and concentration‐dependent blockade of catecholamine release from superfused cells stimulated intermittently with 5 s pulses of 59 m m K + . After 5 min superfusion, a 3 μ m concentration inhibited secretion by 20%; the blockade increased gradually with perfusion time, to reach 85% after 40 min. The IC 50 to block secretion after 5 min periods of exposure to increasing concentrations of R56865 was around 3.1 μ m . The blocking effects of R56865 were reversible after 5–15 min wash out. In high Ca 2+ solution (10 m m Ca 2+ ), the degree of blockade of secretion diminished by 20% in comparison with 1 m m Ca 2+ . 3 In electroporated cells, R56865 (10 μ m ) did not modify the secretory response induced by the application of 10 μ m free Ca 2+ . 4 R56865 blocked the peak I Ba current in a concentration‐ and time‐dependent manner; its IC 50 was very similar to that obtained for secretion (3 μ m ). The compound not only reduced the size of the peak current but also promoted its inactivation; when the effects of R56865 were measured at the most inactivated part of the current, its IC 50 was 1 μ m . Both the inactivation and the reduction of the peak currents were reversible upon washing out the drug. 5 In fura‐2‐loaded single chromaffin cells the basal [Ca 2+ ] i of around 100 n m was elevated to a peak of 1.5 μ m by the application of a 5 s pulse of 59 m m K + . R56865 (10 μ m ) did not affect the basal [Ca 2+ ] i but blocked by 90% the K + ‐evoked increase. This effect was fully reversible after 5–10 min of wash out. 6 The results are compatible with the idea that R56865 blocks Ca 2+ entry into K + ‐depolarized chromaffin cells by promoting the inactivation of voltage‐dependent Ca 2+ channels; this would lead to the limitation of the rise in [Ca 2+ ] i and of the release of catecholamines. The restriction of catecholamine release may favour indirectly the known direct beneficial cardioprotective actions of R56865.