Figure 8.

Putative signaling pathways of autonomic nervous responses. Muscarinic cholinergic and beta-adrenergic pathways involved in autonomic nervous system responses of crucian carp atrial myocytes. Activation of muscarinic cholinergic receptors induces I_K,CCh and inhibits I_Ca via βγ and α_i/o-subunits of the trimeric G protein, respectively. Inhibition of I_Ca is dependent on the tonic activation of adenylate cyclase (AC) under basal conditions, i.e. in the absence of agonist binding to beta-adrenergic receptors (β). Nitric oxide synthase (NOS) is not involved in modulating the responses. Cholinergic activation of I_K,CCh and inhibition of I_Ca results in shortening of action potential and depression of atrial contraction force. GIRK, G protein activated inward rectifier potassium channel; LCC, L-type calcium channel; M2, muscarinic cholinergic receptor; PDE2, phosphodiesterase; PKA, protein kinase A.