ISSN:
1432-2013
Keywords:
Adrenaline
;
α 1-Adrenoceptor
;
Ca2+ release
;
Ca2+-dependent K+ conductance
;
Patch clamp
;
Mouse peritoneal macrophage
Source:
Springer Online Journal Archives 1860-2000
Topics:
Medicine
Notes:
Abstract Responses to adrenaline in mouse peritoneal macrophages were investigated with perforated and cell-attached patch-clamp recording, and with a combination of the perforated-patch recording and fura-2 fluorescence measurements. Extracellularly applied adrenaline induced a transient outward current (4–10s in duration, 100–500 pA in amplitude) at −40 mV associated with a marked increase in conductance. The adrenaline-induced current [I o (Adr)] reversed polarity near −80 mV. The reversal potential depended distinctly on the external K+ concentration but not on external Cl− concentration. Removal of external Ca2+ did not affect I o(Adr) within 2–4 min but subsequent responses to adrenaline were progressively depressed. In contrast, treatment with an intracellular Ca2+ chelator, the acetoxymethyl ester of 1,2-bis-(2-aminophenoxy)ethane-N,N,N′,N′-tetraacetic acid completely abolished I o(Adr). Furthermore, I o(Adr) was blocked by bath-applied quinidine and charybdotoxin, but not by tetraethylammonium or apamin. Extracellular application of an α 1-adrenoceptor agonist phenylephrine and of noradrenaline mimicked I o(Adr). On the other hand, I o(Adr) was antagonized by a non-selective α-adrenoceptor antagonist phentolamine (0.2 μM) and an α 1-adrenoceptor antagonist prazosin (0.2 μM), but was not affected by an α2-adrenoceptor antagonist yohimbine (1 μM) or a β-adrenoceptor antagonist propranolol (1 μM). Cell-attached single-channel recordings with the pipette solution containing 145 mM KCl revealed the activation of single-channel currents with a conductance of 40 pS during application of adrenaline outside the patch. Parallel measurements of membrane current and fura-2 fluorescence in the same cell demonstrated a correlation between the rise in [Ca2+]i and an increase in K+ conductance. Therefore, it is concluded that adrenaline activates a Ca2+-dependent K+ conductance by release of Ca2+ from internal stores through an activation of an α 1-adrenoceptor.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00371119
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