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Calcium regulation in the freshwater‐adapted mummichog
Author(s) -
Patrick M. L.,
Wood C. M.,
Marshall W. S.
Publication year - 1997
Publication title -
journal of fish biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.672
H-Index - 115
eISSN - 1095-8649
pISSN - 0022-1112
DOI - 10.1111/j.1095-8649.1997.tb02519.x
Subject(s) - fundulus , gill , biology , calcium , chloride , ammonia , excretion , acid–base homeostasis , lanthanum , biophysics , zoology , biochemistry , medicine , chemistry , fishery , fish <actinopterygii> , inorganic chemistry , organic chemistry
In light of recent findings of an unusual pattern of ionoregulation (high Na + uptake and negligible Cl ‐ uptake) in the freshwater‐adapted mummichog Fundulus heteroclitus , the pattern of Ca 2+ regulation was examined. Under control conditions (water Ca 2+ = 200μEq l ‐1 ), unidirectional Ca 2+ influx was 11 ± 4 nEq g ‐1 h ‐1 . Acute variation of external Ca 2+ levels revealed a saturable Ca 2+ uptake system with a relatively high affinity ( K m = 125 ± 36 μEq 1 ‐1 ) and a transport capacity ( J max = 31 ± 4 nEq g ‐1 h ‐1 ) comparable to those of other teleosts. Lanthanum (equimolar to [Ca 2+ ]) significantly blocked Ca 2+ uptake by 67% whereas magnesium had no effect. Chronic low Ca 2+ exposure (50 μEq 1 ‐1 ) stimulated Ca 2+ uptake almost three‐fold above control values, whereas chronic high Ca 2+ exposure (20000 μEq 1 ‐1 ) had no effect. Lanthanum and chronic low Ca 2+ treatments disturbed the normally positive Ca 2+ and Na + balances of the animals whereas acid‐base balance and ammonia excretion were undisturbed. The results indicate that Ca 2+ regulation by the mummichog conforms to the model for freshwater Ca 2+ transport whereby chloride cells on the gills take up Ca 2+ actively from the water. However, the absence of extra‐intestinal Cl ‐ uptake and the recent demonstration of significant Ca 2+ uptake by opercular epithelia raise questions about the relative roles of branchial and opercular epithelial chloride cells in freshwater F. heteroclitus .