Effects of channel toxins on <b>Ca²⁺</b> currents in isolated SON neurons.

<p>(<b>A</b>) Isolated magnocellular neurons were identified as either vasopressin or oxytocin by their presence or absence of the GFP signal. Scale bar = 10 µm. (<b>B</b>) The current-voltage relationships show no difference between whole-cell calcium currents (WCCC) of vasopressin and oxytocin neurons (n = 20 each). (<b>C</b>) Normalized conductance (G/G_max, fitted using Boltzmann equation) showed no significant change with or without TG. (<b>D</b>) Examples of two neurons (both oxytocin neurons), one vehicle treated (•) and one 50 min after pre-treating with thapsigargin (○). The steady-state Ca²⁺ current is plotted against time following treatment with channel toxins (in order: 1 µM nicardipine; 200 nM ω-agatoxin IV; 500 nM ω-conotoxin GVIA). The current measured after each toxin was subtracted from that evoked before each treatment to determine the current carried by L-, P/Q- and N-type channels. The remaining current was attributed to R-type channels. (<b>E</b>) Examples of N-, L- and WCCC elicited by voltage steps in controls and TG treated cells. (<b>F</b>) The resulting current density for each current type normalised for the peak maximal current was averaged (n = 5) to give the average current density from neurons treated with vehicle or thapsigargin. (<b>G</b>) In a subsequent experiment L- or N-type channel toxins were administered, alternating the order (n = 5 for each condition). Mean±S.E.M are shown and compared by t-test. *<i>P</i><0.05 vs control.