ENHANCED EXCITATORY JUNCTION POTENTIALS IN MESENTERIC-ARTERIES FROM SPONTANEOUSLY HYPERTENSIVE RATS

Excitatory junction potentials (EJPs) were examined using intracellula r recording techniques in mesenteric arteries isolated from 12- to 15- week-old spontaneously hypertensive (SHR), Wistar Kyoto (WKY and Sprag ue Dawley (SD) rats. The amplitudes of EJPs evoked by single supramaxi mal stimuli were larger in arteries from SHRs (12.9+/-0.7 mV, n = 16) than in arteries from either WKYs (5.2+/-0.5 mV, n = 24) or SDs (8.6+/ -0.8 mV, n = 15). The time constant of decay of EJPs did not differ si gnificantly, suggesting that the passive electrical properties of the vascular smooth muscle are similar in the three rat strains. Spontaneo us EJPs recorded in tissues from SHRs and WKYs had similar amplitude f requency distributions, suggesting that the quantal size is also simil ar between strains. In some arteries from SHRs, EJPs evoked by single stimuli triggered muscle action potentials (MAPs). Visible constrictio n only occurred following a MAP. In tissues from all three strains, su mmation of EJPs triggered MAPs. As EJPs are generated by the sympathet ic co-transmitter adenosine 5'-triphosphate (ATP), the findings of the present study indicate that purinergic transmission is enhanced in me senteric arteries from SHRs, probably as a result of an increase in qu antal release. A consequence is that when nerves are activated SHR art eries more readily undergo constriction that is dependent on voltage-a ctivated Ca2+ influx.