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FLUX OF CALCIUM ACROSS THE SHEEP RUMEN WALL IN VIVO AND IN VITRO
Author(s) -
Höller H.,
Breves G.,
Gerdes Herta,
Kocabatmaz M.
Publication year - 1988
Publication title -
quarterly journal of experimental physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.925
H-Index - 101
eISSN - 1469-445X
pISSN - 0144-8757
DOI - 10.1113/expphysiol.1988.sp003180
Subject(s) - rumen , flux (metallurgy) , calcium , in vivo , in vitro , zoology , chemistry , biology , food science , microbiology and biotechnology , biochemistry , fermentation , organic chemistry
Experiments were carried out in vivo and in vitro to study the flux of Ca 2+ across the sheep rumen wall. Buffer solutions with five different Ca 2+ , concentrations in the range 0·2‐3·6 mmol l −1 were introduced into the isolated, emptied and washed reticulo‐rumen for 1 h to determine Ca 2+ net flux. Phosphate concentrations were either kept constant at 8 mmol l −1 , or varied so as to maintain a constant phosphate/Ca 2+ ratio of 2:1. Under both conditions there was a Ca 2+ net secretion into the rumen at Ca 2+ concentrations below approximately 1 mmol l −1 whereas Ca 2+ net absorption occurred at higher Ca 2+ concentrations and linearly increased with increasing Ca 2+ concentrations. When phosphate concentrations were reduced to 4·3 and 0·6 mmol l −1 (Ca 2+ , 3 mmol l −1 ) Ca 2+ net absorption was reduced by about 50% and completely abolished, respectively. The unidirectional (mucosal‐to‐serosal or serosal‐to‐mucosal) Ca fluxes in vitro, J Ca ms and J Ca sm , were measured in Ussing chambers with computer‐controlled voltage clamp. Under short‐circuit current conditions (Ca 2+ and phosphate, 2 mmol l −1 ) there was a significant net flux of Ca 2+ from the mucosal to the serosal side. This net flux of Ca 2+ was abolished when ouabain was added to the serosal solution, indicating that the unidirectional Ca 2+ flux J Ca ms and, hence, the net flux of Ca 2+ was dependent upon active Na + transport accomplished by the Na, K‐ATPase system. Under voltage clamp conditions, the net flux of Ca 2+ was greatly increased at a potential difference PD = ‐25 mV (serosa negative) but disappeared at PD = +25 mV (serosa positive). Analysis of the unidirectional Ca 2+ fluxes J Ca ms and J Ca sm under varying potential differences indicated that both Ca 2+ fluxes consisted of a PD‐dependent and a PD‐independent component. The results show that the reticulo‐rumen participates in Ca 2+ absorption in sheep.