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Long‐term potentiation of transmitter release induced by adrenaline in bull‐frog sympathetic ganglia.

Long‐term potentiation (l.t.p.) of transmitter release induced by adrenaline in bull‐frog sympathetic ganglia was studied using intracellular recording techniques. The quantal content of the fast excitatory post‐synaptic potentials (fast e.p.s.p.s: evoked by the nicotinic action of acetylcholine) was potentiated for more than several hours after treatment with adrenaline (1‐100 microM). A similar l.t.p. of quantal content was produced consistently by isoprenaline (10 microM) and only in a certain fraction of cells by dopamine (10 microM). The l.t.p. induced by adrenaline (10 microM) was blocked by a beta‐antagonist, propranolol (1 microM), but not by an alpha‐antagonist, phenoxybenzamine (1 microM). Dibutyryl adenosine 3',5'‐phosphate (dibutyryl cyclic AMP) (0.8‐1.0 mM), adenosine 3',5'‐phosphate (cyclic AMP) (4 mM), 3‐isobutyl‐1‐methylxanthine (10 microM), caffeine (1‐2 mM), and cholera toxin (2 micrograms ml‐1) applied for 20‐30 min, all caused the l.t.p. of quantal content. By contrast, adenosine 5'‐phosphate (AMP) (4 mM) and adenosine (4 mM) had no potentiating action. Treatment of the ganglion with adrenaline (2.5‐160 microM) or dibutyryl cyclic AMP (4 mM) for 15‐30 min resulted in the l.t.p. of the frequency of miniature e.p.s.p.s. The l.t.p. of quantal content induced by adrenaline was markedly suppressed by lowering temperature from 20‐25 degrees C to 11‐13 degrees C, and blocked by dibutyryl guanosine 3',5'‐phosphate (dibutyryl cyclic GMP) (100 microM) consistently when applied together, but inconsistently when given after adrenaline. The post‐synaptic sensitivity to acetylcholine was unchanged for at least 1 h after exposure to adrenaline (2.5‐160 microM) or dibutyryl cyclic AMP (0.8‐4 mM). It can be concluded that adrenaline produces l.t.p. of transmitter release by activating a cyclic‐AMP‐dependent metabolic process through the activation of beta‐adrenoceptors, and that this mechanism is presumably regulated by a process involving endogenous guanosine 3',5'‐phosphate (cyclic GMP).