On the membrane potential independent mechanism of the sodium pump-induced inhibition of spontaneous electrical activity of japanese land snail neurons

1. 1. The dependence of excitability on pump activity of bursting pacemaker of Japanese land snail neurons was studied. 2. 2. The incubation of neurons in potassium-free solution, in spite of the fact that the membrane was hyperpolarized, the frequency of bursting activity was increased and sometimes the interburst hyperpolarization fully disappeared. 3. 3. The 4 mM potassium or rubidium pump activation after preincubation of the neurons in potassiumfree solution leads to transient inhibition of bursting activity independent of the membrane potential level. 4. 4. Adrenaline has a potentiation effect on the potassium-induced inhibition of electrical activity after preincubation of the neurons in the potassium free solutions. This effect of adrenaline was absent in ouabain containing medium. 5. 5. Increasing the external medium tonicity has an inhibitory effect on electrical activity of neurons. 6. 6. It was suggested that the pump-induced cell volume changes could be one of the membrane potential independent mechanisms by which Na-K pump could modulate the membrane excitability.