ABSTRACT
The effects of calmidazolium (10(-7) mol/l) and db cAMP (10(-3) mol/l) on the longitudinal internal resistance (ri) in the rabbit sinus node strips were studied by means of microelectrode and extracellular recording techniques. Calmidazolium (CDZ) decreased ri by 27%. An addition of db cAMP to the CDZ-containing Tyrode potentiated this effect by further 14%. db cAMP initially decreased ri by 17%, then it enhanced this resistance by 7% above the pretreatment control value. An addition of CDZ to the db cAMP-containing Tyrode reduced ri by 41% below the pretreatment control. Possible mechanisms underlying these effects were discussed in terms of cAMP, Cai, and calmodulin action on the cell coupling.
Subject(s)
Bucladesine/pharmacology , Cell Communication/drug effects , Enzyme Inhibitors/pharmacology , Imidazoles/pharmacology , Sinoatrial Node/physiology , Animals , Cell Membrane/drug effects , Cell Membrane/physiology , Electric Conductivity , Membrane Potentials/drug effects , Rabbits , Sinoatrial Node/cytology , Sinoatrial Node/drug effectsABSTRACT
The effect of several concentrations of 7-0-hemisuccinyl, 7-deacetyl forskolin on ri was studied by means of microelectrode and single sucrose gap techniques. Twenty mumol.l-1 of forskolin added to the sucrose gap lowered ri by 15% below the control value. The drug applied at 50 mumol.l-1 initially decreased ri by 31%, and then it increased the resistance by 43% above the control value. The possible mechanisms underlying these effects are discussed in terms of cAMP and Ca action on the cell coupling.
Subject(s)
Colforsin/pharmacology , Sinoatrial Node/drug effects , Animals , Cyclic AMP/physiology , Electric Conductivity , In Vitro Techniques , Intercellular Junctions/drug effects , Intercellular Junctions/physiology , Rabbits , Sinoatrial Node/physiology , Synaptic Transmission/drug effects , Synaptic Transmission/physiologyABSTRACT
The effect of dibutyryl cyclic AMP as well as dibutyryl cyclic GMP on the longitudinal internal resistance was studied in the rabbit sinus node strips by means of microelectrode and sucrose gap techniques. Dibutyryl cyclic AMP added to the sucrose gap decreased the resistance and increased the spontaneous rate whereas dibutyryl cyclic GMP evoked the opposite effects. These results suggest that cyclic nucleotides influence the cell coupling in the sinus node.
Subject(s)
Bucladesine/pharmacology , Cyclic GMP/analogs & derivatives , Dibutyryl Cyclic GMP/pharmacology , Sinoatrial Node/drug effects , Animals , Electrophysiology , In Vitro Techniques , Rabbits , Time FactorsABSTRACT
The longitudinal internal as well as external resistance was measured by means of simultaneous intracellular and sucrose gap voltage recordings. The longitudinal internal resistance could be calculated from a formula comprising the shunt resistance, membrane action potential and transgap action potential before and after shunting. The longitudinal external resistance was calculated from another formula comprising the same quantities.
