Dibutyryl cGMP, like acetylcholine, shortens and reduces repolarization and overshoot of the action potential, slightly hyperpolarizes the cell and decreases the force of the contraction in the atrial working muscle. It suggests that cGMP may mediate the action of acetylcholine in the atrial working fibres.

Acetylcholine↗

PubMedDate not supplied

Effect of exogenous cAMP in the rabbit right auricle.

Isotonic solution of cAMP-Na was applied into spontaneously beating auricular fibres by a cut-end method. Cyclic AMP enhanced the spontaneous rate (mean 48%) and increased the contractile tension (mean 297%). These results provided direct evidence that cAMP is involved in the spontaneous activity and contraction in the heart muscle.

Animals↗

PubMedDate not supplied

Use of fibrin glue in sucrose gap method.

Isolated frog nerves or rabbit sinus node strips were mounted in a single sucrose gap chamber. A fibrin glue Tissucol was used in this arrangement as an intercompartment seal. Under such conditions, the specimens produced stable trans-gap action potentials of relatively high amplitude. In other experiments the gap was filled with fibrin in place of sucrose solution. The results obtained in the fibrin gap experiments resembled these mentioned above.

Action Potentials↗

PubMedDate not supplied

Membrane channel blockers impair cell coupling in the rabbit sinus node strips.

Barium ions, (-) verapamil or tetrodotoxin added to the sucrose gap increased the longitudinal internal resistance in the rabbit sinus node strips. The possible mechanism of these effects are discussed.

Animals↗

PubMedDate not supplied

Effects of forskolin on the longitudinal internal resistance (ri) in rabbit sinus node strips.

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.

Animals↗

PubMedDate not supplied

Effects of cyclic nucleotides on the longitudinal internal resistance in the rabbit sinus node.

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.

Animals↗

PubMedDate not supplied