Unique effect of tetrapentylammonium ions on sympathetic transmission in rat vas deferens.
1. Effects of tetrapentylammonium ions (TPA+) on contractile responses induced by electric field stimulation and by exogenous agonist such as noradrenaline, ATP and high K+ were examined in the isolated epididymal half of the rat vas deferens. 2. The electrically evoked monophasic contractions (0.5 Hz, 1 ms pulse duration, 40 V) were potentiated by TPA+ at low concentrations (1-3 microM) and inhibited by TPA+ at a concentration greater than 10 microM. 3. TPA+ (0.3-3 microM) potentiated the contractile responses induced by noradrenaline and ATP, whilst, TPA+ (10 microM) concentration-dependently reduced the agonist-induced contractions. TEA+ enhanced both electrically evoked and agonist-induced contractions. 4. TPA+ (0.3 microM) potentiated 30 mM K+-induced phasic contraction which was inhibited by pretreatment with alpha,beta-methylene ATP (3 microM) and prazosin (3 microM). 5. TPA+ (10-300 microM) reduced the contractions induced by 100 mM extracellular K+ while TBA+ and TEA+ had no effect. 6. The present results show that TPA+ at low concentrations may act at prejunctional nerve membranes to enhance release of contractile transmitters and act as a putative K+ channel blocker at postjunctional membranes to increase muscle contractility in rat vas deferens; whilst at high concentrations TPA+ mainly acts on smooth muscle probably as a non-selective relaxant against the agonist-induced contraction probably through inhibition of Ca2+ influx; this inhibitory effect appears unique for TPA+ since TEA+ and TBA+ did not induce muscle relaxation.
Huang
Y
Y
Department of Physiology, Faculty of Medicine, Chinese University of Hong Kong, Shatin, China.
Lau
C W
CW
D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000037:antagonists & inhibitors; D004305:Dose-Response Relationship, Drug; D004558:Electric Stimulation; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009469:Neuromuscular Junction / Q000187:drug effects*; D009638:Norepinephrine / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D011224:Prazosin / Q000494:pharmacology; D000644:Quaternary Ammonium Compounds / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D009435:Synaptic Transmission / Q000187:drug effects*; D014649:Vas Deferens / Q000187:drug effects* / Q000294:innervation
D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D000644:Quaternary Ammonium Compounds; D000255:Adenosine Triphosphate; C027435:tetrapentylammonium; C002630:alpha,beta-methyleneadenosine 5'-triphosphate; D011188:Potassium; D002118:Calcium; D009638:Norepinephrine; D011224:Prazosin