Abstract
In Hydra vulgaris, discharge of stenotele nematocysts was induced by contact with prey, electrical stimuli, or increase in the external potassium concentration. In each case 10-4 M calcium was required in the culture medium. The results indicated a voltage- and calcium-dependent mechanism different from mechano- or chemoreception allowing calcium influx from the external medium. A threshold for activation was suggested by the steep increase of the rate of electrically induced discharge in external fields of 3.5 kV/m. Although organic antagonists for vertebrate calcium channels were ineffective in blocking the calcium-induced nematocyst discharge, inorganic divalent and trivalent cations competitively inhibited the process, with a sequence (Co2+ < Ni2+ < Cd2+ < La3+ < Gd3+) similar to that seen for antagonism of calcium influx through voltage-dependent channels. Magnesium, an intracellular calcium antagonist, decreased nematocyst discharge, while strontium replacing calcium supported the discharge at a lowered rate. It is concluded that in the nematocyte a voltage-activated influx of calcium through apical ion channels initiates the discharge of the nematocyst in an exocytotic process.
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Gitter, A.H., Oliver, D. & Thurm, U. Calcium- and voltage-dependence of nematocyst discharge in Hydra vulgaris . J Comp Physiol A 175, 115–122 (1994). https://doi.org/10.1007/BF00217442
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DOI: https://doi.org/10.1007/BF00217442