The Ca2+ currents (ICa) recorded by the whole-cell patch clamp technique were examined in mature neurons cultured in defined medium from the principal neurosecretory system of decapod crustaceans, the X-organ - sinus gland. After 1 day, X-organ neurons of the crab, Cardisoma carnifex, showed vigorous outgrowth with broad lamellipodia (veils) or, from smaller somata, branching morphology. The veilers had large ICa (~650 pA, ~5 µA/cm2) while the others had little or no ICa. After 5-6 days, similar differences were present. However, morphologies observed after additional outgrowth, when correlated with ICa responses, supported distinguishing four groups: 1) veilers and 2) branching veilers, which developed from veilers and had similar ICa density (~3 µA/cm2); and, developing from the 1-day branchers, 3) spiny branchers or 4) small cells (ICa density ~0.8 µA/cm2). Immunoreactivity indicative of crustacean hyperglycemic hormone was present in all veilers and branching veilers tested; molt-inhibiting hormone reactivity, when observed, was seen in cells having robust ICa density (>1.2 µA/cm2). Normalized average current-voltage curves for each morphological group were compared and were examined for changes with time in culture. The curves were consistent with ICa controlled by a population of high-voltage-activated Ca2+ channels whose properties are biophysically indistinguishable and do not change with time in culture. The peak ICa remained the same, despite outgrowth of the neurons, resulting in a reduction of ICa density. Thus, additional Ca2+ channels were apparently not added with addition of new membrane under our culturing conditions.
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