Sodium transport in salamander proximal tubule at 5.5 degrees C.
Na+ transport and electrophysiology of isolated perfused proximal tubules of the salamander Ambystoma tigrinum were compared at 22 and 5.5 degrees C, a range over which these animals normally live. Both intracellular Na+ activity and basolateral membrane potential were unaffected by temperature, whereas transepithelial potential depolarized from -6.5 +/- 0.8 mV at 22 degrees C to -3.5 +/- 0.6 mV at 5.5 degrees C (P less than 0.05). Compared with 22 degrees C, reduction of temperature to 5.5 degrees C included major increases in apical membrane resistance (2,052 +/- 473 omega.cm2 to 18,464 +/- 2,667 omega.cm2) and basolateral membrane resistance (491 +/- 113 omega.cm2 to 1,780 +/- 256 omega.cm2) (P less than 0.01). Sequential increases of luminal glucose concentration allowed characterization of the Na(+) -glucose cotransporter at both temperatures. The Km was stable (2 mM), but the maximal activity (Vmax) at 5.5 degrees C of 167 peq/5 cm2 increased to 1,000 peq/5 cm2 at 22 degrees C (P less than 0.05). In parallel with this temperature sensitivity of apical Na+ entry, basolateral Na+ pump activity was reduced at low temperature. Rubidium uptake at 22 degrees C was reduced by 40% at 5.5 degrees C. The rate of decrease of intracellular Na+ activity when tubules were perfused with substrate-free solution was -2.6 +/- 0.7 mM/min at 5.5 degrees C, compared with -4.9 +/- 1.2 mM/min at 22 degrees C. We conclude that low temperature reduces both Na+ uptake and efflux, allowing stability of intracellular milieu despite reduction in net transepithelial transport.
Morgunov
N S
NS
Department of Physiology and Biophysics, Dalhousie University, Halifax, Nova Scotia, Canada.
Hirsch
D J
DJ
D000557:Ambystoma; D000818:Animals; D001692:Biological Transport; D003080:Cold Temperature; D005947:Glucose / Q000378:metabolism; D066298:In Vitro Techniques; D007687:Kidney Tubules, Proximal / Q000378:metabolism*; D009004:Monosaccharide Transport Proteins / Q000378:metabolism; D010042:Ouabain / Q000494:pharmacology; D012044:Regression Analysis; D012413:Rubidium / Q000493:pharmacokinetics; D012964:Sodium / Q000378:metabolism*
D009004:Monosaccharide Transport Proteins; D010042:Ouabain; D012964:Sodium; D005947:Glucose; D012413:Rubidium