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

Temperature perturbation was used to determine whether increased turnover of Na, K, and Cl at 37 degrees 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 42K, 36Cl, and 24Na (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 42K and 36Cl effluxes in DOCH differed from controls. At 20 degrees 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 degrees C. These results indicate that alterations in resting 42K, 36Cl, and 24Na 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 42K and 36Cl effluxes in DOCH at 37 degrees C persisted in aortas that had undergone cold storage for 2 days before incubation at 37 degrees 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.