[Membrane potential and transport of neuromediators in synaptosomes of the brain of rats with spontaneous hypertension].

The transport of 3H-GABA, 14C-choline, 14C-noradrenaline and 3H-serotonin in brain synaptosomes of spontaneously-hypertensive rats (SHR) which is controlled by the carrier whose activity is dependent on the sodium gradient and electric potential of the plasma membrane was studied. The initial rate of GABA uptake by SHR synaptosomes was reduced by 25%. The steady state of the content of GABA, noradrenaline and serotonin in SHR synaptosomes was reduced by 15-20%, whereas the steady state of choline content by 35%. The differences are levelled when synaptosomes are depolarized, both due to the elimination of K+-diffusion potential, and the opening of Na channels. An increase in the extracellular calcium concentration up to 1 mmol results in a 20% synaptosomal GABA rise that is unrelated to membrane hyperpolarization. In the presence of the Ca-ionophore A-23187, a similar effect is observed with a 1-2 mmol Ca2+ concentration. The electric potential of SHR synaptosomes which is studied by means of the fluorescent dye dis-C3-(5) was shown to be reduced by 5-10 mV. Partial depolarization of SHR synaptosomes is supposed to be the principal cause of the decrease in both the initial rate of uptake and the steady state of the content of neuromediators.