Role of microtubules in the adaptive response to low phosphate of Na/Pi cotransport in opossum kidney cells.
The role of microtubules and actin microfilaments in adaptive changes of the apical Na-dependent transport of phosphate (Pi) was investigated in opossum kidney (OK) cells. Up-regulation of Na/Pi cotransport was achieved by incubating OK cells in a medium containing 0.1 mM Pi; down-regulation of Na/Pi cotransport was provoked by refeeding adapted cells with 2 mM Pi. Up-regulation of Na/Pi cotransport was found to be inhibited by approximately 50% after a pretreatment of the cells with the microtubule disrupting agents nocodozole and colchicine; indirect immunofluorescence indicated complete depolymerization of the microtubular network. No inhibition of the adaptive response was observed after treatment of the cells with cytochalasin B to depolymerize actin microfilaments. In adapted cells, depolymerization of microtubules by nocodozole led to a reversibility of Na/Pi cotransport similar to that observed after refeeding adapted cells with 2 mM Pi. No effects of the microtubule disrupting drugs were observed on Na/L-glutamic acid transport. Depolymerization of microtubules did not prevent parathyroid-hormone-mediated inhibition of Na/Pi cotransport. It is concluded that microtubules are (at least in part) involved in the correct insertion of newly synthesized apical Na/Pi cotransport systems and that microtubules are not involved in the internalization of Na/Pi cotransport systems.
Hansch
E
E
Institute of Physiology, University of Zürich-Irchel, Switzerland.
Forgo
J
J
Murer
H
H
Biber
J
J
D008841:Actin Cytoskeleton / Q000378:metabolism; D000199:Actins / Q000378:metabolism; D000222:Adaptation, Physiological / Q000502:physiology*; D000818:Animals; D002478:Cells, Cultured; D003078:Colchicine / Q000494:pharmacology; D003571:Cytochalasin B / Q000494:pharmacology; D003599:Cytoskeleton / Q000378:metabolism; D015536:Down-Regulation / Q000187:drug effects; D005455:Fluorescent Antibody Technique; D017136:Ion Transport / Q000502:physiology*; D007668:Kidney / Q000378:metabolism*; D008870:Microtubules / Q000502:physiology*; D009893:Opossums / Q000378:metabolism*; D010710:Phosphates / Q000172:deficiency* / Q000378:metabolism; D012964:Sodium / Q000378:metabolism*; D015854:Up-Regulation / Q000187:drug effects
D000199:Actins; D010710:Phosphates; D003571:Cytochalasin B; D012964:Sodium; D003078:Colchicine