[Transport of monovalent thallium across the membrane of oocyte of the lamprey Lampetra fluviatilis].

Mechanisms of transport of monovalent thallium across the membrane of oocyte of the lamprey Lampetra fluviatilis were studied by using 204Tl. Transport of Tl+ in lamprey oocytes has been shown to be realized by at least two pathways: through Na/K-pump and by the mechanism of Na,K,Cl-cotransport. In the standard Ringer solution (mM): 4 KCl, 140 NaCl, 0.5 CaCl2, 5 glucose, 10 Tris-HCl--in the presence of oubain, the coefficient of the 204Tl stationary distribution (cell/medium) was within the range of 2.3-2.5, while the time necessary to reach its 50 % value amounted to 40-5 min at 20 degrees C. In potassium-free media, transport of 204Tl via Na/K-pump was described by simple kinetis with saturation and was characterized by the value V(max) = 520 pmol/(cell x h) and K(M) = 0.3 mM. In the presence of 4 mM K+ and 0.1 mM/l Tl+, the oubain-sensitive Tl+ flow decreased to 75 pmol/(cell x h). At activation of the mechanism of Na,K,Cl-cotransport by the outer Na+ (in Na-NMDG media of different composition) the total inflow of Tl+ reached 193 +/- 20 pmol/(cell x h), while the butamenide-sensitive component--119 +/- 12 pmol/(cell x h) with K(M) for Na+ about 20 mM. In the incubation media with variable concentration of chloride ions (replacement of Cl- by NO3(-)) the total Tl+ flow reached 220 +/- 21, while via the mechanisms of Na,K,Cl-cotransport--87 +/- 8 pmol/(cell x h). Under our experimental conditions, mechanisms of active transport and Na,K,Cl-cotransport accounted for 94% of the Tl+ inflow. The potassium channels that usually are also permeable to monovalent thallium ions were not revealed.