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Blockade of the inotropic effect of Bay K 8644 by cytochalasin‐B and phloretin
Author(s) -
Dresel Peter E.,
Ogbaghebriel Azieb
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.tb11560.x
Subject(s) - phloretin , nitrendipine , chemistry , inotrope , papillary muscle , endocrinology , medicine , calcium , atrium (architecture) , biology , biochemistry , atrial fibrillation
1 The positive inotropic effect in rabbit atria and papillary muscles of Bay K 8644 is blocked by cytochalasin‐B (Cyto‐B) and phloretin, two compounds known to block the facilitated diffusion of glucose. These compounds do not change the concentration‐response curve of calcium. 2 Cyto‐B is more potent in atria than in papillary muscles, 10 −7 m having a maximal effect in atria whereas 2 × 10 −5 m was required for a maximal effect in papillary muscles. Phloretin was fully effective at 10 −4 m , the only concentration tested. 3 The inotropic effect of Bay K 8644 was virtually abolished in atria bathed in a glucose‐free medium or one containing 5 mM pyruvate. The contractile response to Bay K 8644 of papillary muscles was not changed significantly in glucose‐free or in pyruvate‐containing medium. 4 Cyto‐B (2 × 10 −5 m ) caused a slight but significant increase in the K D for the binding of nitrendipine to a crude sarcolemnal preparation from rabbit ventricles. The B max was unchanged. 5 These results may best be explained by the hypothesis that there is a metabolic requirement for the inotropic effect of Bay K 8644.