Regenerative electrical activity and arterial contraction in hypertensive rats

Isolated tail arteries from spontaneously hypertensive rats-stroke prone strain (SHRSP) display oscillatory contractile responses to norepinephrine. These oscillations are not observed in tail arteries from normotensive Wistar-Kyoto rats (WKY). The mechanism underlying these oscillatory contractions was investigated by simultaneous measurement of isometric force development and membrane potential (E_m) from tail artery strips in vitro. After equilibration in physiological salt solution containing 1.6 mM calcium (37° C), resting E_m was not different between WKY (−52±1.1 mV) and SHRSP (−52±0.4 mV). Norepinephrine (3×10⁻⁷ M) produced a similar degree of depolarization in tissues from the two strains (WKY=−42.5±0.9, SHRSP=−41±0.8). However, while E_m recordings from WKY arteries were quiescent, those from SHRSP displayed bursts of electrical spiking activity that were temporally associated with the rising phase of oscillations in contractile force. The frequency and duration of these bursts of action potentials increased with the concentration of norepinephrine. Action potentials were not observed in calcium-free solution or in the presence of nifedipine (3×10⁻⁷ M). Releasing the passive stretch on the tissues caused a decrease in the rate of spiking. These studies demonstrate catecholamine-induced regenerative electrical activity in tail arteries from SHRSP that is dependent on extracellular calcium. This activity is unique to tail arteries from this strain.