Insulin depolarizes plasma membrane and induces voltage-gated Ca²⁺ influx in NG neurons.

<p><b><b><i>A and B</i></b></b>: Administration of 10⁻⁷ M insulin depolarized the membrane potential in NG neurons under perforated-patch configuration (<i>A</i>). The results are representative of 5 neurons. The membrane potentials before, during and after insulin treatment (<i>B</i>, n = 5) ** p<0.01 by one-way ANOVA followed by Turkey’s test. <b><i>C</i></b>: Administration of 10⁻⁷ M insulin twice induced repeated [Ca²⁺]_i increases in single NG neurons. The data are representative of 53 neurons. <b><i>D∼F</i></b>: Insulin-induced [Ca²⁺]_i increases were markedly suppressed by L- and N-type Ca²⁺ channel blockers, 10 µM verapamil (<i>D</i>) and 0.5 µM ω-conotoxin GVIA (ω-Cono; <i>E</i>), respectively, and abolished under a Ca²⁺-free condition added with 0.1 mM EGTA (<i>F</i>). The data are representative of 25 neurons in (<i>D</i>), 15 in (<i>E</i>) and 28 in (<i>F</i>). <b><i>G</i></b>: The ratio of the peak [Ca²⁺]_i response to the first insulin stimulation (S1) over that to the second insulin stimulation (S2) under control and test conditions. The numbers on each bar indicate the numbers of neurons that responded to insulin. Different letters above bars indicate significant difference, <i>P</i><0.05 by one-way ANOVA followed by Tukey’s test.