Negative inotropic effect of cyclic GMP in cardiac fiber fragments.

The force of spontaneously beating cardiac cellular fragments obtained from mice heart by homogenization was recorded in presence of cyclic guanosine -3'.5'-monophosphate (cGMP) and cyclic 8-bromguanosine -3'.5'-monophosphate in concentrations of 3 X 10(-6) M - 33 X 10(-6) M. The nucleotide decreased the force and reduced the rate of spontaneity. Eventually the preparation became quiescent. It is thought that this nucleotide either reduces the capacity to sequester calcium or affects its release from the sarcotubular system.