RELEASE OF NORADRENALINE AND ATP BY ELECTRICAL-STIMULATION AND NICOTINE IN GUINEA-PIG VAS-DEFERENS

Effects of electrical stimulation and nicotine on ATP and tritium outflow and smooth muscle tension were studied in the guinea-pig isolated vas deferens preincubated with [H-3]-noradrenaline. ATP was measured using the luciferase technique. Electrical stimulation caused biphasic contractions and an acceleration of ATP and tritium outflow. The contraction amplitude and the overflow of ATP increased markedly, whereas the overflow of tritium increased only slightly with the frequency of stimulation (1-10 Hz; constant number of 60 pulses). The contraction amplitude did not increase with an increase in pulse number (20-540 pulses; constant frequency of 5 Hz), whereas the overflow of ATP increased slightly, and that of tritium markedly. Nicotine caused monophasic, transient contractions and, again, an acceleration of ATP and tritium outflow. Contractions, ATP and tritium overflow increased with the concentration of nicotine (56-320-mu-mol/l) in an approximately parallel manner. The influence of some drugs on responses to electrical stimulation (60 pulses, 5 Hz) and nicotine (180-mu-mol/l) was investigated. Tetrodotoxin blocked all effects of electrical stimulation but did not change those of nicotine. The reverse was true for hexamethonium. Neither electrical stimulation nor nicotine caused contraction or an increase in ATP outflow after pretreatment with 6-hydroxydopamine. The main effects of prazosin 0.3-mu-mol/l were to reduce electrically evoked contractions (above all second phase) as well as nicotine-evoked contractions and the nicotine-evoked overflow of ATP (the latter by about 81%). Prazosin also tended to diminish the electrically evoked overflow of ATP. Alpha,beta-methylene-ATP 10-mu-mol/l elicited a transient contraction and ATP overflow on its own. The main change in the subsequent state of desensitization was a decrease of the first phase of electrically evoked contractions. The main effects of prazosin combined with desensitization by alpha,beta-methylene-ATP were marked decreases of electrically evoked contractions (by 94%), the electrically evoked overflow ATP (by 66%), nicotine-evoked contractions (by 97%) and the nicotine-evoked overflow of ATP (by 70%). It is concluded that both electrical stimulation and nicotine release noradrenaline and ATP in guinea-pig vas deferens. Only part of the evoked overflow of ATP (about 32%) is neural in origin. Another part probably originates from smooth muscle cells where it is released by neurogenic noradrenaline acting at alpha-1-adrenoceptors. Corelease leads to cotransmission:electrically as well as nicotine-evoked contractions consist of adrenergic and purinergic components. Varying types of stimulation release cotransmitter mixtures of varying composition. Electrical stimulation at high frequency (for example 10 Hz) and with low pulse numbers (for example 20 pulses) seems to release the cotransmitters at a relatively high ATP/noradrenaline ratio. Activation of prejunctional nicotine receptors seems to release the cotransmitters at a relatively low ATP/noradrenaline ratio.