Effects of calmidazolium, carbachol and derivatives of cyclic GMP on the longitudinal internal resistivity in rabbit atrial trabeculae.

The effects of calmidazolium, carbachol and membrane permeable derivatives of cGMP (dipalmitoyl cGMP and 8-Bromo cGMP) on the longitudinal internal resistivity (Ri) were studied in the rabbit atrial trabeculae by means of electrophysiological recording techniques and histological planimetry. Calmidazolium as well as carbachol decreased Ri whereas cGMP-derivatives enhanced this resistivity. The effect of calmidazolium suggested that calmodulin reduced the cell coupling under control conditions. Carbachol decreased the Ca-inward current, and probably it prevented the calmodulin activation. The action of the nucleotides showed that cGMP did not mediate the cholinergic effect on the cell coupling. The possible interaction between calmodulin and cGMP was discussed.