Temperature dependence of transcellular and intracellular parameters of frog skin

Studies on the mechanism(s) for temperature dependence of sodium transport in tight epithelia reported in literature, have primarily been derived from transcellular studies. No attempts were made to discriminate between trans and paracellular conduction pathways nor is it possible from such measurements to examine the contribution of the apical and/or basolateral cellular membranes to the overall temperature dependency of the transport process. In this study we report on the temperature dependence of intracellular as well as transcellular parameters. Using a specific protocol, which provides the temperature coefficients for the amiloride displaceable sodium current, cellular conductance and the apical and basolateral membrane, conductances. Temperature coefficients derived from the slopes of Arrhenius plots of these parameters were found to be very similar (9-10 KCal/mole). The intracellular potential before and after amiloride showed weak temperature dependence (less than 1 mV/degrees C), however. On the basis of our results here, and in view of certain theoretical considerations, we conclude that the inhibition of Na+ transport across frog skin by decreasing the temperature is primarily due to a decrease in the permeability of the apical and basolateral membranes. This decrease in permeability is brought about by changes in the viscosity of water and the radius of the moving particle; in this case sodium plus hydration shell. The effect of temperature on the intracellular potential could be partially accounted for by changes in the equilibrium-potential for potassium and in part to changes in the rheogenic transport component for sodium across the basolateral membrane.