Regulation of Potential-Dependent Ca2+ Channels by Serotonin 5-HT1B Receptors in Different Populations of Hippocampal Neurons

Abstract

Metabotropic serotonin 5-HT1 receptors in cerebral neurons have a role in regulating such emotional states in humans as aggression, fear, and alcohol addiction. Activation of presynaptic 5-HT1B receptors leads to suppression of Ca2+ influx via potential-dependent calcium channels in certain neurons. Ca2+ influx into cells was measured in terms of the increase in the cytosolic calcium ion concentration in response to depolarization induced by addition of 35 mM KCl. An image analysis system showed that Ca2+ responses to depolarization of cultured hippocampal cells differed in terms of shape, rate, and amplitude in different neuron populations. 5-HT1B receptor agonists produced minor suppression of the activity of potential-dependent calcium channels in 86 ± 3% of neurons. Two minor cell populations (5–8% of cells each) were seen, which differed strongly in terms of the extent of desensitization of the Ca2+ signal. The calcium signal of one cell population responded to depolarization with a characteristic delay and a high rate of quenching. 5-HT1B receptor agonists produced powerful inhibition of the amplitude of the Ca2+ response to KCl only in this population. The calcium signal of the second population of cells was characterized by the absence of densensitization. 5-HT1B receptor agonists produced minor increases in the amplitude of the calcium response to depolarization in this population of neurons. Thus, these studies demonstrated differences in the serotonin 5-HT1B receptor sensitivities of potential-dependent calcium channels in different neuron populations.