Influence of temperature on stimulus‐secretion coupling in the sympathetic nerves and on neuromuscular transmission, in guinea‐pig vas deferens

Publisher Website
Google Scholar
Abstract
In guinea‐pig isolated vas deferens moderate cooling (within the range 16–41 °C) improved, while further cooling depressed, sympathetic neuromuscular transmission. Moderate cooling: (a) enhanced the contractile responses both to electrical nerve stimulation and (although less strongly) to exogenous noradrenaline or to the adenosine 5′‐triphosphate (ATP) analogue, α, β‐methylene ATP; (b) enhanced the overflow of [3H]noradrenaline evoked by electrical nerve stimulation at 1–8 Hz, but not that caused by direct depolarization of varicosities with 80 mM potassium; (c) reduced the depressing effect of exogenous noradrenaline, as well as the enhancing effect of the a‐adrenoceptor blocking agent phentolamine, on the secretory responses to electrical nerve stimulation; (d) while not altering the maximal secretion of tracer noradrenaline at infinitely high frequency or external calcium, lowered the frequency or calcium concentration required for half‐maximal secretion, both in the absence and in the presence of phentolamine. In conclusion: moderate cooling improves sympathetic neuromuscular transmission in guinea‐pig vas deferens, both prejunctionally, by enhancing transmitter secretion, and post‐junctionally, by increasing the responsiveness of the smooth muscle to transmitter.