P-CTX-1B produces a transient Na⁺-dependent cytosolic Ca²⁺ increases in bovine chromaffin cells.

<p>(A) Optical sections of a confocal-imaged chromaffin cell pre-loaded with fluo-3/AM following the addition of P-CTX-1B (10 nM) to a 2 mM Ca²⁺-containing medium (time in sec indicated in the figure). Scale bar: 10 µm. (B) Relative variation of fluo-3 fluorescence (F/F₀) determined, as a function of time, in a Ca²⁺-containing medium (black curve, representative of n = 12 cells) or in a Ca²⁺-free medium added with 2 mM EGTA (red curve, representative of n = 6 cells). (C) Same experiment as in A, but chromaffin cells were pre-treated with TTX (1 µM for 15 min) prior to addition of P-CTX-1B to a Ca²⁺-containing medium. High K⁺ was added to the medium after 2 min (last image). Scale bar: 10 µm. (D) Fluorescence variation showing that TTX abolishes the ciguatoxin-induced fluorescence increase. High K⁺-induced depolarization of the cell still produces a robust fluorescence increase.