title: Are there any presynaptic 5-HT receptors in frog atria?
abstract: The effect of 5-hydroxytryptamine (5-HT) on the stimulation-induced inotropic responses was investigated in the isolated frog atria and ventricles. 5-HT (1 X 10(-5)-2 X 10(-4) M) inhibited the contractile responses elicited by intramural nerve stimulation (INS) in atria. The inhibitory action of 5-HT was antagonized by raising the external Ca++ concentration. Pizotifen and methysergide (1 X 10(-6) M) antagonized the inhibitory action of 5-HT on high frequency INS responses. Higher concentrations of methysergide by itself depressed the responses to low frequency INS. Ketanserin, metoclopramide and phentolamine (1 X 10(-6) M) failed to antagonize the inhibitory action of 5-HT. The results suggest that the inhibitory effect of 5-HT in frog atria is mediated through a subtype of 5-HT receptors which is neither of 5-HT2 nor of "M" type but may correspond to the 5-HT1 subtype of serotoninergic receptors. In contrast with atria, 5-HT-induced inhibition of INS responses was not observed in frog ventricles.
mesh_terms: D000818:Animals; D001001:Anura; D002118:Calcium / Q000494:pharmacology; D004558:Electric Stimulation; D004837:Epinephrine / Q000494:pharmacology; D006325:Heart Atria / Q000294:innervation*; D066298:In Vitro Techniques; D007650:Ketanserin / Q000494:pharmacology; D008297:Male; D008784:Methysergide / Q000494:pharmacology; D009200:Myocardial Contraction / Q000187:drug effects; D009469:Neuromuscular Junction / Q000187:drug effects; D010646:Phentolamine / Q000494:pharmacology; D017981:Receptors, Neurotransmitter / Q000502:physiology; D011985:Receptors, Serotonin / Q000502:physiology*; D009435:Synaptic Transmission / Q000187:drug effects
chemical_list: D017981:Receptors, Neurotransmitter; D011985:Receptors, Serotonin; D007650:Ketanserin; D002118:Calcium; D008784:Methysergide; D004837:Epinephrine; D010646:Phentolamine