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THE EFFECTS OF THE CALCIUM IONOPHORE, A23187, ON THE AXOPLASMIC TRANSPORT OF DOPAMINE β‐HYDROXYLASE
Author(s) -
ESQUERRO E.,
GARCIA A.G.,
SANCHEZGARCIA P.
Publication year - 1980
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/j.1476-5381.1980.tb08713.x
Subject(s) - ionophore , calcium , chemistry , axoplasm , axoplasmic transport , biophysics , free nerve ending , extracellular , axon , medicine , biochemistry , endocrinology , anatomy , biology , organic chemistry
1 The effects of the ionophore, A23187, on the intra‐axonal transport of dopamine β‐hydroxylase (DBH) were investigated in the cat hypogastric nerve‐inferior mesenteric ganglion preparation by monitoring, in vitro , the enzyme accumulation above a ligature, 2 to 2.5 cm distal to the ganglion. 2 DBH accumulation in the proximal segment immediately above the ligature (P 1 ) increased linearly up to 6 h, during incubation in normal Krebs solution at 37°C. The ionophore, A23187, interfered with the enzyme accumulation, but did not modify the previously accumulated DBH activity present in P 1 . 3 The blocking effects of A23187 on DBH transport were greatly impaired in the absence of extracellular calcium ions; an excess of calcium in the bathing solution (7.5 mM) itself blocked the enzyme transport by 50%. 4 A23187 did not significantly modify the levels of adenosine triphosphate (ATP) in the segments P 1 and P 2 of the nerve proximal to the ligature. 5 Nerves incubated in an A23187‐containing medium showed many mitochondria of normal shape and fine structure; however, typical microtubules or filaments were not seen in these preparations. 6 The results suggest that the ionophore A23187, by considerably raising the axoplasmic ionized calcium levels, interferes with the assembling of microtubules. In this manner, the ionophore would inhibit the transport of adrenergic vesicles and therefore of DBH along the axon. The results also provide additional evidence in favour of the view that for the transport system to work adequately, it is necessary to maintain the intra‐axoplasmic ionized calcium concentration between certain critical levels.