Volume regulation of nerve terminals.
Pinched-off presynaptic nerve terminals (synaptosomes) possess significant regulatory volume increase (RVI) and regulatory volume decrease (RVD) capabilities. Following a swelling induced by a hypotonic challenge, the synaptosomes regulate their volume and adjust it, in 2 min, to within 5% of its initial value (RVD) at an initial rate of -0.77 +/- 0.10%/s (mean +/- SEM). Following a shrinking induced by a hypertonic challenge, the synaptosomes also regulate their volume at an initial rate of 0.18 +/- 0.02%/s (RVI), resulting in a new steady state, reached within 5-10 min, with a synaptosomal volume below the original volume. The omission of Na+ or K+ ions from the extrasynaptosomal medium reduces the initial rate of RVI by 72.5 and 66.5%, respectively. The "loop diuretics" bumetanide and furosemide significantly inhibited the RVI of the synaptosomes. In contrast, ouabain, amiloride, or 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid did not have any significant effect on RVI parameters. Furthermore, bumetanide-sensitive 86Rb uptake by rat brain synaptosomes was stimulated threefold by a hypertonic perturbation of 30%. Thus we conclude that the RVI of synaptosomes is mainly due to a stimulation of the Na+, K+, Cl- co-transport system induced by the synaptosomal shrinking following the hypertonic challenge.
Babila
T
T
Department of Physiology, Hebrew University-Hadassah Medical School, Jerusalem, Israel.
Atlan
H
H
Fromer
I
I
Schwalb
H
H
Uretzky
G
G
Lichtstein
D
D
D000818:Animals; D002034:Bumetanide / Q000494:pharmacology; D002352:Carrier Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D007038:Hypotonic Solutions / Q000494:pharmacology; D008297:Male; D008565:Membrane Proteins / Q000378:metabolism; D009411:Nerve Endings / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D012413:Rubidium / Q000378:metabolism; D012414:Rubidium Radioisotopes; D028021:Sodium-Potassium-Chloride Symporters
D002352:Carrier Proteins; D007038:Hypotonic Solutions; D008565:Membrane Proteins; D012414:Rubidium Radioisotopes; D028021:Sodium-Potassium-Chloride Symporters; D002034:Bumetanide; D012413:Rubidium