Spontaneous Electrical Activity in Pressurized Small Mesenteric Arteries

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Abstract
Spontaneous electrical activity was recorded intracellularly in vitro from smooth muscle cells of guinea pig small pressurized mesenteric arteries. Spontaneous action potentials were recorded at 37 °C at frequencies of 30–55/min. Each action potential consisted of a prepotential (pacemaker potential) followed by a spike of variable amplitude (10–35 mV). This activity was not blocked by tetrodotoxin (TTX) or guanethidine, indicating it was myogenic in origin. Sympathetic nerve stimulation (single 0.5-ms field stimuli) could evoke action potentials in between the spontaneous action potentials and could drive the activity; this effect was blocked by TTX. Addition of the vasodilator adenosine (10–6 to 10–4M) reversibly decreased action potential amplitude and frequency. Lowering the temperature to 35 °C for 1–3 min during a single impalement decreased spontaneous action potential frequency. Spontaneous activity was abolished after longer periods at 35 °C. The spontaneous activity recorded in vitro at 37 °C and 5 or 40 mm Hg inflation pressure was similar to that previously reported from guinea pig and rat mesenteric arteries in vivo. Such activity might be important in the normal physiological control of arterial tone.