<prompt> Activation of postsynaptic M2 receptors on the hea is associated withActivation of adenylyl cyclaseOpening of NaK cation channelsDecrease in cAMP formationIncrease in IP3 and DAG  <response>: M2 and M4 receptors act by the opening of K channels. M1 and M4 act by the IP3-DAG pathway. 