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Effects of cadmium on the slow inward current of frog heart muscle in relation to a lowering of pH in external solution
Author(s) -
Pater Christine,
Sauviat MartinPierre
Publication year - 1988
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.1476-5381.1988.tb11549.x
Subject(s) - tetrodotoxin , chemistry , biophysics , cadmium , sucrose gap , grenouille , reversal potential , dissociation constant , rana , electrophysiology , membrane potential , analytical chemistry (journal) , endocrinology , medicine , patch clamp , biochemistry , salientia , chromatography , biology , xenopus , receptor , organic chemistry , gene
1 The effect of cadmium (Cd) on the slow inward current (I si ) of frog atrial fibres was studied by the double sucrose gap technique. 2 Cd (5μ m ) depressed I si in a voltage‐dependent manner without alteration of the apparent reversal potential for I si . 3 Dose‐response curves indicated an apparent dissociation constant for the Cd blocking effect of 4.5 μ m at 0 mV, with a one to one relationship between Cd and the slow channel. 4 Increasing the external concentration of Ca ions ([Ca] 0 ) in the tetrodotoxin (TTX)‐containing Ringer solution antagonized the block of I si by Cd. Double reciprocal plots for I si versus [Ca] 0 drawn in the presence or in the absence of Cd intersected at the ordinate, indicating that Cd competes with Ca for a common binding site. 5 Lowering the external pH from 7.3 to 6.3 depressed I si . The block caused by H was voltage‐dependent. Double reciprocal plots for I si versus [Ca] o drawn at pH 7.3 and 6.3 intersected at the abscissa, and indicated that H and Ca did not compete for a common site. 6 Lowering the external pH did not change the ability of Cd to inhibit I si . 7 The data suggested the existence of two different sites within the slow channel in frog atrial fibres, one of them being H‐sensitive and the other cadmium‐sensitive.