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Cytochalasin D reduces Ca 2+ currents via cofilin‐activated depolymerization of F‐actin in guinea‐pig cardiomyocytes
Author(s) -
Rueckschloss U.,
Isenberg G.
Publication year - 2001
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1111/j.1469-7793.2001.00363.x
Subject(s) - phalloidin , chemistry , actin , dephosphorylation , biophysics , cytochalasin d , depolymerization , cytochalasin , cofilin , intracellular , cytochalasin b , biochemistry , phosphatase , actin cytoskeleton , cytoskeleton , phosphorylation , biology , cell , organic chemistry
1 L‐type Ca 2+ channel currents ( I Ca ) were measured in guinea‐pig ventricular myocytes (22 °C, 300 ms steps from ‐45 to +10 mV). Pulsing at 0.5 Hz reduced I Ca within 5 min to 92 ± 3 % (mean ± s.e.m. , n = 14 ) and within 10 min to 83 ± 4 % (‘run‐down’ with reference to I Ca after a 5 min equilibration period). 2 Bath‐applied cytochalasin D (cytD, 10 μ m ) reduced I Ca to 75 ± 4 % within 5 min and to 61 ± 4 % within 10 min (‘cytD reduction of I Ca ‘) by reduction of maximal Ca 2+ conductance (suggested by fits of time course and of current‐potential ( I–V ) curves). 3 Preincubation with phalloidin (bath applied, 100 μ m , 5 h) prevented the cytD reduction of I Ca . Since phalloidin specifically blocks F‐actin depolymerization, cytD reduction of I Ca is linked to depolymerization of F‐actin. 4 CytD did not attenuate the β‐adrenergic stimulation of I Ca (30 n m isoproterenol), suggesting that A kinase anchoring proteins are unlikely to mediate the cytD reduction of I Ca . The cytD reduction of I Ca was abolished by extra‐/intracellular acidosis (pH o 6.9), by cell dialysis of 5 m m BAPTA, or by serine/threonine protein phosphatase inhibitors. 5 Actin‐depolymerizing factor (ADF)/cofilin are proteins that bind to actin, mediate a pH‐sensitive depolymerization of F‐actin, and are activated by dephosphorylation. Western blots from hearts perfused with solutions containing zero or 10 μ m cytD indicated that cytD reduces the ratio of phosphorylated to total ADF/cofilin content by 50 %. 6 The data support the concept that cytD mediates dephosphorylation and activation of ADF/cofilin, leading to depolymerization of F‐actin with a subsequent reduction of I Ca .