Ca dependence of Na influx during treatment of rabbit aorta with NE and high K solutions
- St. George's Hospital Medical School, London (England) Univ. of Missouri School of Medicine, Columbia (USA)
Cellular influx of {sup 24}Na was measured in isolated rabbit aorta during stimulation with 10 {mu}M norepinephrine (NE) or depolarization with 80 mM K solution, using a pulse-labeling, cold-wash technique. NE caused a two- to threefold increase in Na influx; a smaller but significant increase was also observed in depolarized tissues. Basal and Ne-induced fluxes at 1 min were significantly increased by a 20-min preincubation in a Ca-free solution containing 2 mM EGTA; elevation of (Mg) in this solution reduced these effects. The high K-induced influx was prevented by a combination of low Ca (30 {mu}m) and elevated Mg (10 mM). The Ca agonist, BAY-K 8644, increased {sup 24}Na influx. The Ca antagonist, diltiazem, inhibited the depolarization-stimulated {sup 24}Na influx in a concentration-dependent manner, but was less effective in blocking the response to NE. Extension of the preincubation in NE plus Ca-free medium from 30 s to 15 min decreased the influx response and contraction. After exposure to NE in Ca-free solution, {sup 24}Na influx remained elevated 10 min after washing out NE in the continued absence of Ca. A second exposure to NE at that time did not increase influx. The authors propose that a component of {sup 24}Na influx during excitation depends directly on a rise in intracellular (Ca). The role of an indirect effect of (Ca) on metabolic H{sup +} production with subsequent stimulation of the Na{sup +}-H{sup +} exchange may also be a factor.
- OSTI ID:
- 6937774
- Journal Information:
- American Journal of Physiology; (USA), Journal Name: American Journal of Physiology; (USA) Vol. 254:1; ISSN 0002-9513; ISSN AJPHA
- Country of Publication:
- United States
- Language:
- English
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