Temperature dependence of ionic transport and norepinephrine stimulation of rat aorta during DOCA hypertension.

Abstract

SUMMARY Temperature perturbation was used to determine whether increased turnover of Na, K, and Cl at 37° C in aortas from rats made hypertensive with deoxycorticosterone acetate salt treatment (DOCH) reflects an increased number of transport sites that individually maintain relatively normal function. Decreasing temperature reduced the resting effluxes of 42 K, ^Cl, and M Na (active and passive) from control and DOCH in parallel fashion. The slope of the Arrhenius plots (activation energies) and the transition temperatures at which major changes in slope occurred were similar in controls and DOCH. In contrast to the results for resting effluxes, the temperature dependence for the effects of norepinephrine (NE) on contraction and on K and "^Cl effluxes in DOCH differed from controls. At 20° C, the responses to NE were either abolished or greatly suppressed in DOCH, as compared to controls, while no significant differences between the two groups were observed at 30° C. These results indicate that alterations in resting 42 K, -"Cl, and 24 Na effluxes in DOCH may result from an increased number of transport sites in the membranes of vascular smooth muscle. The concept that alterations occurred in the integral components of the membrane is also supported by the observation that increased resting 42 K and Cl effluxes in DOCH at 37° C persisted in aortas that had undergone cold storage for 2 days before incubation at 37° C. The altered temperature dependence for the effects of NE on DOCH, compared to controls, indicates that the involvement of agonist-receptor-membrane events may be dissociated from the alterations in resting ionic fluxes. K occurred in the aorta and femoral arteries from rats made hypertensive either with deoxycorticosterone acetate (DOCA) or aldosterone.1 -2 The net exchange of cellular Na and K in tail arteries for extracellular Li also proceeded at a faster rate in DOCA hypertensive rats.3 One important consequence of such alteration would be to increase the leak of ions along their electrochemical gradient, which would lead to altered excitability. In addition to these passive movements, evidence exists for an inFrom the Department of Physiology, University of Missouri at Columbia, Columbia, Missouri 65212.