Parallel changes in ultrastructure and noradrenaline content of nerve terminals in rat vas deferens following...

Transmural electrical stimulation and exposure to incubation media where some or all of the Na+ had been replaced with K+ were used to elicit transmitter release. Changes in noradrenaline content and ultrastructure of the nerve terminal varicosities in rat vas deferens were measured. Electrical stimulation in the presence of 4-aminopyridine had little effect, but high [K+] solutions caused a parallel reduction in noradrenaline content and the number of small dense-cored vesicles; large dense-cored vesicles showed no change, and small clear vesicles increased in number. In spite of a reduction in total vesicle number there was no evidence of expansion of the varicosity membrane. The parallel fall in noradrenaline content and in the number of small dense-cored vesicles suggests that the latter are the source of the released noradrenaline under the conditions of high [K+] stimulation we have used.