Influence of cyclic nucleotides on junctional permeability in atrial muscle.

The influence of dB-cAMP (5 X 10(-4) M) and 8-Br-cGMP (5 X 10(-5) M; 5 X 10(-9) M) on the longitudinal diffusion of Lucifer Yellow CH along dog trabeculae was investigated. It was found that dB-cAMP enhances the diffusion coefficient of the dye from 4 +/- 0.63 X 10(-7) cm2/s (control) to 2 +/- 0.53 X 10(-6) cm2/s. Efflux studies showed that the permeability of the surface cell membrane to Lucifer Yellow is negligible ruling out the possibility that the dye moved from cell-to-cell through the extracellular space. The permeability of the nexal membrane (Pnexus = 3 X 4 cm/s) was appreciably enhanced in fibers exposed to dB-cAMP (9.1 X 10(-4) cm/s). No change in the longitudinal redistribution of Lucifer Yellow CH was found with 8-Br-cGMP. The results support the hypothesis that cAMP is a modulator of junctional permeability in the normal heart.