Inhibitory action of norepinephrine on sodium transport in vascular smooth muscle cells in culture

Action of azelastine on intracellular Ca2+ in cultured airway smooth muscle

Azelastine, a novel antiasthmatic/antiallergic agent, was tested for Ca2+ antagonistic properties in cultured rabbit airway smooth muscle, vascular smooth muscle and cardiocytes. In airway smooth muscle cells, the basal cytosolic free calcium content was 195 +/- 72 nM (mean +/- S.D., n = 18). These basal values were decreased by azelastine with an IC50 value of 1.1 +/- 0.3 x 10(-4) M. Endothelin-1 (10(-7) M) induced a rapid increase in free cytosolic calcium up to 806 +/- 314 nM, which returned to normal levels in 3-5 min. This was fully blocked by azelastine in a concentration-dependent manner, with an IC50 value of 6.7 +/- 2.9 x 10(-5) M. Moreover, azelastine fully blocked histamine-induced calcium mobilization (IC50 = 7 x 10(-5) M). In cultured vascular smooth muscle cells and cardiocytes, azelastine was unable to decrease the basal cytosolic free calcium content or inhibit agonist-induced calcium mobilization. Therefore, at therapeutic levels, a specific, mild inhibition of calcium mobilization in airway smooth muscle may be one component of the antiasthmatic action of azelastine.

Regulation of Na+ and K+ contents in rat thymocytes

A modified nystatin technique allowed the investigation of the initial rate of Na+ efflux as a function of internal Na+ content under steady-state conditions in rat thymocytes. This kinetic study showed that 1) ouabain-sensitive Na+ efflux as a function of internal Na+ can be adjusted by a three-sites kinetic model, with a maximal pump rate of 581 +/- 79 mmol.l cells-1.h-1 and an apparent dissociation constant for internal Na+ of 10.0 +/- 1.0 mmol/l cells (mean +/- SE of 3 experiments), 2) bumetanide-sensitive Na+ efflux was extremely low compared with the pump efflux (approximately 1%), and 3) ouabain- and bumetanide-resistant Na+ efflux was almost a linear function of internal Na+ content (as expected for a Na+ leak). This "all-pump" mechanism of thymocyte Na+ regulation was confirmed by non-steady-state experiments showing that 1) ouabain induced a rapid net Na+ gain and K+ depletion in fresh thymocytes and completely blocked the recovery of normal cation contents in Na+-loaded-K+-depleted thymocytes, and 2) bumetanide was unable to modify thymocyte Na+ and K+ contents. Na+ extrusion by Na+-loaded thymocytes was unaffected by prostaglandin E2, isoproterenol, or platelet-aggregating factor (PAF) and was slightly impaired in the adult spontaneously hypertensive rat of the Okamoto strain (10% lower rate constant for net Na+ extrusion, P less than 0.05). Concerning cell Na+ regulation, our results do not support the concept that rat thymocytes are more representative of vascular cells than enucleated erythrocytes.