Stopped-Flow Microperfusion Studies of Urate Absorption from the Rat Proximal Tubule

Abstract

Abstract

The absorptive flux of [2-¹⁴C]urate in the rat proximal tubule was examined using stopped-flow and continuous-flow microperfusion techniques. In the stopped-flow studies, the luminal perfusion was a steady-state equilibrium solution and the luminal contact time was 60 sec. The ratio of disintegrations per minute (dpm) of urate in the reaspirated sample to the initial solution (C/I) was 0.42 ± 0.02 in control experiments. The addition of either phloridzin or ρ-chloromercuribenzoate to the perfusion solution resulted in significantly higher C/I ratios of 0.52 ± 0.03 (P < 0.05) and 0.61 ± 0.006 (P < 0.01), respectively. Substitution of choline for sodium in the perfusion solution or the addition of probenecid did not significantly change the C/I ratio. In continuous-flow microperfusion studies, the fractional absorption of urate from an isotonic saline solution averaged 10.2 ± 0.8%/mm tubule and was significantly inhibited by the addition of probenecid to the perfusion solution. Urate absorption from a steady-state perfusion solution averaged 4.7 ± 1.0%/mm tubule (P < 0.01 compared to the saline solution) and was not affected by the addition of probenecid. These studies indicate that the presence of either phloridzin or ρ-chloromercuribenzoate in the solution bathing the luminal side of the rat proximal tubule cells inhibits urate absorption. Neither the substitution of choline for sodium in the perfusion solution nor the addition of probenecid to the perfusion solution had any significant effect. The failure to demonstrate an effect of probenecid in the stopped-flow studies may have been due to the requirement to use a non-water absorbing solution. When water absorption is permitted to occur, the addition of probenecid to the perfusion solution inhibited urate absorption.