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Cotransmitters in the motor nerves of the guinea pig vas deferens: electrophysiological evidence.
Sneddon P; Westfall DP; Fedan JS
Science 1982 Nov; 218(4573):693-695
The effects of arylazido aminoproprionyl adenosine-triphosphate (AA ATP) and prazosin (19216569) were investigated on the excitatory junction potential (EJP) of guinea-pig vas deferens muscles. Intracellular microelectrodes filled with potassium-chloride were used to record EJP evoked by stimulation of the prostate and of the vas deferens by two platinum electrode rings. Pulse width was 0.5 millisecond. The vas deferens was mounted in a continuously suffused organ bath. The tissue was photolyzed for 20 minutes in the presence of 0.0004 moles of AA ATP and after. AA ATP was removed. Tissues treated with light for the same period without AA ATP served as controls. AA ATP treatment produced an irreversible antagonism of phosphate receptor mediated response. At 0.5 Hertz (Hz) the average value for EJP was about 8.6 milliVolts (mV) before AA ATP and 2.5mV afterward. AA ATP treated tissue stimulated at 5Hz gave an EJP of about 6.6mV. Light controls showed no significant changes from the untreated group. The contractile response of the vas deferens was biphasic. AA ATP depressed phase 1 of the response but not phase 2. Prazosin reduced phase 2 of the contractile response. This reaction indicated the involvement of the alpha receptors in the neurotransmission process. Prazosin was also selective for alpha post synaptic receptors and increased EJP at doses that abolished phase 2 of the contraction. This showed that phase 2 was independent of membrane depolarization. AA ATP treatment did not alter summation of EJP. To explain the mechanism of action, the authors propose that, on stimulation, adenosine- triphosphate or a related purine is released from motor nerves to produce EJP, which produce five action potentials that cause phase 1 of the contractile response.
NIOSH-Author; Physiological-response; Adrenocortical-hormones; Biological-effects; Neuromuscular-system; Electrical-stimulation; Electrophysiological-measurements; Muscle-contraction; Neurophysiology; Nerve-fiber-excitation
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