THE SPONTANEOUS AND EVOKED RELEASE OF SPERMINE FROM RAT BRAIN in vitro

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Abstract
1 The efflux of previously accumulated [3H]-spermine from brain slices was measured using a continuous perfusion system. The spontaneous efflux was biphasic, consisting of an initial rapid efflux followed by a much slower release. 2 The slices were depolarized by the addition to the medium of high potassium concentrations, ouabain or veratrine. 3 At concentrations greater than 30 mM, potassium evoked a striking increase in the release of [3H]-spermine. Following uptake in the presence of 5.7 × 10−9M[3H]-spermine, K+-evoked release was dependent on the presence of calcium ions. Release of spermine after uptake at 5.6 × 10−8m or 5.0 × 10−7m was not calcium-dependent. 4 The calcium-dependent, K+-stimulated release of spermine was inhibited in the presence of diphenylhydantoin (5 × 10−3m) or ruthenium red (10−3 m). 5 Following uptake of 5.7 × 10−9m [3H]-spermine in a sodium-free medium, the calcium-dependent, K+-stimulated release was significantly inhibited. 6 Ouabain (10−4m) caused a large but calcium-independent increase in the efflux of [3H]-spermine. 7 Veratrine-induced release was less substantial but was increased in a calcium-free medium. Release evoked by veratrine was abolished in the absence of sodium. 8 These results are discussed with respect to a possible ‘neurotransmitter’ or ‘neuromodulator’ role for spermine.

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