Mechanism of norepinephrine release elicited by Na+-K+ adenosine triphosphatase inhibition in the isolated rat kidney: involvement of voltage-dependent Ca++ channels.

The mechanism by which ouabain and Na+ depletion enhance the release of norepinephrine (NE) was investigated in the isolated rat kidney prelabeled with [3H]NE by examining the efflux of tritium elicited by these stimuli during 1) Ca++ depletion and 2) administration of tetrodotoxin, amiloride and Ca++ channel blockers. In kidneys perfused with Tyrode's solution containing low K+ solution (0.54 mM), ouabain (10(-4) M) enhanced tritium efflux markedly by about 20-fold at 30 min. Depletion of Na+ from the perfusion medium also produced an increase in tritium overflow which peaked at 20 min. Administration of tetrodotoxin (0.3 microM) inhibited the effect of ouabain, but not that of Na+ depletion, to increase tritium efflux and perfusion pressure. In contrast, amiloride (180 microM) enhanced the overflow of tritium elicited by ouabain but failed to alter that elicited by Na+ depletion. The rise in perfusion pressure caused by both stimuli was attenuated by amiloride. Omission of Ca++ (1.8 mM) from the perfusion medium inhibited the increase in tritium efflux and perfusion pressure elicited by ouabain and Na+ depletion by 80 and 65%, respectively. The Ca++ channel blockers omega-conotoxin (50 nM), diltiazem (60 microM) and flunarizine (2 microM), but not nifedipine (1.4 microM), inhibited tritium overflow elicited by ouabain. However, nifedipine, diltiazem and flunarizine, but not omega-conotoxin attenuated the tritium overflow elicited by Na+ depletion. The rise in perfusion pressure elicited by ouabain in low K+ and Na+ depletion was inhibited by these Ca++ channel blockers.(ABSTRACT TRUNCATED AT 250 WORDS)