Conduction block in Purkinje fibers by homogeneous versus localized decrease of the gap junction conductance.

Gap junction channels provide the pathway for the cell-to-cell propagation of cardiac action potential. Impairment of junctional conductance decreases conduction velocity and can cause block, two conditions that favor ventricular arrhythmias and fibrillation by re-entrant excitation. These experiments were designed to examine the effects of homogeneous versus localized decrease of the gap junction conductance on propagation of action potential in Purkinje fibers from sheep hearts.

Synergy between two calcium channel blockers, verapamil and fantofarone (SR33557), in reversing chloroquine resistance in Plasmodium falciparum.

This study describes the synergistic interaction of two calcium channel blockers, verapamil (VR) and SR33557 or fantofarone (SR), in reversing chloroquine resistance in Plasmodium falciparum, the causative agent of human malaria. The two calcium channel blockers exhibited an intrinsic antimalarial activity at 10 and 1 microM for verapamil and fantofarone, respectively. Isobolograms revealed that chloroquine and verapamil, and chloroquine and fantofarone, acted synergistically against chloroquine-resistant strains of P.

Regulation of gap junctional communication during human trophoblast differentiation.

During pregnancy, the trophoblast, supporting the main functions of the placenta, develops from the fusion of cytotrophoblastic cells into a syncytiotrophoblast. Gap junction channels consisting of connexins link the cytosols of cells in contact. Gap junctional communication has been involved in the control of cell and tissue differentiation.

Contraceptive gossypol blocks cell-to-cell communication in human and rat cells.

Gossypol (a polycyclic lipophilic agent naturally present in cottonseed, known as a potent non-steroid antifertility agent and a non-specific enzyme inhibitor) irreversibly impaired the intercellular communication between homologous pairs of various cultured cells, from man or rat, involved (Sertoli or trophoblastic cells) or not involved (ventricular myocytes) in steroidogenesis, in a dose-dependent manner. In serum-free assays, a rapid junctional uncoupling occurred in non-cytotoxic conditions. At 5 microM (approximately twice the peak plasma concentration measured in human patients during chronic administration), gap junctional communication was interrupted within 4 to 10 min, without concomitant rise in the intracellular Ca2+ concentration.