Excitatory junction potentials (e.j.p.s) were recorded from smooth muscle cells of the saphenous arteries of young rabbits. 2. The amplitudes of e.j.p.s recorded from different preparations, in response to a single maximal stimulus, were small and variable (5--14 mV). They decayed exponentially with a time constant of about 200 msec. 3. At frequencies greater than 1 Hz the shape of those e.j.p.s which exceeded 12--15 mV in amplitude was changed. The early part of the e.j.p.s became faster in time course. 4. Trains of up to five stimuli, at frequencies greater than 4 Hz, caused summation of e.j.p.s; 'active responses' were superimposed on this depolarization. Peak amplitude of the response to repetitive stimulation was 50 mV. 5. In normal solution, contraction appeared to be associated with a change in the configuration of e.j.p.s. 6. No action potentials resembling those recorded from most visceral smooth muscles were observed in normal solutions although these could be evoked in the presence of TEA (2.5--10 mM). 7. The method of Abe & Tomita (1968) was used to determine the values of the length constant (lambda) and time constant (tau) of the smooth muscle of intact arteries. The value of lambda (0.6 mm) was about half that found for circular strips cut from larger arteries. 8. The time constant of decay of single e.j.p.s of less than 12 mV in amplitude was indistinguishable from the membrane time constant. 9. Noradrenaline caused contraction of the artery in the absence of a change in membrane potential. 10. It is tentatively suggested that there may be two different populations of receptors in this smooth muscle membrane.
