pH‐dependent transport of procainamide in cultured renal epithelial monolayers of OK cells: consistent with nonionic diffusion

Abstract

1 Previous studies suggest that procainamide is a substrate for organic cation/proton antiport. In order to study the coupling between procainamide flux and proton flux in greater detail we investigated the effects of extracellular procainamide addition upon intracellular pH in cultured monolayers of renal 5 Procainamide efflux from procainamide-loaded cell monolayers resulted in a significant acidification of intracellular pH. As with procainamide uptake, this result could be ascribed to the movement of neutral weak base. 6 These effects of procainamide upon intracellular pH are consistent with nonionic diffusion of procainamide rather than an interaction of procainamide with the organic cation/proton antiporter. In addition, the results suggest that organic cation/proton antiport is not highly expressed in OK cells.

Mediation of cimetidine secretion by P‐glycoprotein and a novel H+‐coupled mechanism in cultured renal epithelial monolayers of LLC‐PK1 cells

“…Furthermore from these experiments we can conclude that the permeability of the apical membrane to the unionised form of cimetidine must be small since at pH 7.4 and at pH 8.4, where almost all the cimetidine is in the unionised form (80% at pH 7.4, 97.5% at pH 8.4) we see no effect upon intracellular pH. This contrasts with the marked effect upon intracellular pH found with other weak bases such as procainamide where permeation of the unionised form of weak base across the apical membrane followed by a reduction in intracellular proton concentration as the weak a 6.6 -6.8 _-I.. base becomes protonated results in an intracellular alkalinisation (Dudley & Brown, 1995).…”

“…To do this, we have measured both transepithelial fluxes and initial rates of [3H]-cimetidine uptake across the apical and basolateral membranes of cultured LLC-PK, cells grown on permeable filter supports. In addition we have investigated the coupling of cimetidine transport to proton flux using the pH-sensitive fluorescent probe 2',7' -bis(2 -carboxyethyl) -5(6) -carboxyfluorescein (BCECF) (Dudley & Brown, 1995). The results suggest that cimetidine secretion across the apical membrane of LLC-PKI cells is mediated primarily by P-glycoprotein.…”

The organic cation transporter OCT2 mediates the uptake of β‐adrenoceptor antagonists across the apical membrane of renal LLC‐PK1 cell monolayers

“…In a previous study, we demonstrated the potential of measurement of intracellular pH as a tool to characterize the relative contribution of charged and uncharged forms of a weak base to its overall transport ( Dudley & Brown, 1995 ; 1996 ). In this study, we set out to characterize the handling of the weak base metoprolol and related β‐adrenoceptor antagonists at the apical and basolateral membranes of epithelial monolayers of cultured renal LLC‐PK 1 cells.…”

“…Intracellular pH (pH i ) was measured as previously described ( Thwaites et al ., 1993 ; Dudley & Brown, 1995 ). Briefly, cell monolayers grown on 12 mm diameter filter supports were loaded by incubation with BCECF‐AM (5 μ M ) in both the apical and basolateral chambers for 40 min at 37°C in culture media.…”

“…Many drug molecules are weak bases, and exist in both charged (organic cation) and uncharged (neutral weak base) forms. Recently we reported that measurement of intracellular pH (pH i ) could be used as a powerful technique to differentiate between the transport of the charged organic cation and diffusion of the neutral weak base ( Dudley & Brown, 1995 ; 1996 ). In this study, we have characterized the transport of a range of structurally related β‐adrenoceptor antagonists across monolayers of LLC‐PK 1 cells, by measuring the effect of drug addition upon intracellular pH.…”