The mycotoxin ochratoxin A deranges pH homeostasis in Madin-Darby canine kidney cells

Abstract

Ochratoxin A (OTA) is a nephrotoxin which blocks plasma membrane anion conductance in Madin-Darby canine kidney (MDCK) cells. Added to the culture medium, OTA transforms MDCK cells in a manner similar to exposure to alkaline stress. By means of video-imaging and microelectrode techniques, we investigated whether OTA (1 mumol/liter) affects intracellular pH (pHi), Cl- (Cl-i) or cell volume of MDCK cells acutely exposed to normal (pHnorm = 7.4) and alkaline (pHalk = 7.7) conditions. At pHnorm, OTA increased Cl-i by 2.6 +/- 0.4 mmol/liter (n = 14, P < 0.05) but had no effect on pHi. At pHalk, application of OTA increased Cl-i by 8.6 +/- 2.6 mmol/liter (n = 10, P < 0.05) and raised pHi by 0.11 +/- 0.03 (n = 8, P < 0.05). The Cl-/HCO3- exchange inhibitor DNDS (4,4'-dinitro-stilbene-2,2'-disulfonate; 10 mumol/liter) eliminated the OTA-induced changes of pHi and Cl-i. OTA did not affect cell volume under both pHnorm and pHalk conditions. We conclude that the OTA-induced blockade of plasma membrane anion conductance increases Cl-i without changing cell volume. The driving force of plasma membrane Cl-/HCO3- exchange dissipates, leading to a rise of pHi when cells are exposed to an acute alkaline load. Thus, OTA interferes with pHi and Cl-i homeostasis leading to morphological and functional alterations in MDCK cells.

Blockade of swelling‐induced chloride channels by phenol derivatives

“…Greger and coworkers demonstrated that in epithelial cells, NPPB added to the extracellular fluid is three orders of magnitude more potent than A9C (Wangemann et al, 1986). Ochratoxin A was also demonstrated to be able to block chloride channels in epithelial cells and shows a structural similarity to NPPB (Wdll et al, 1993;Gekle et al, 1993 (Paulmichl et al, 1993;Gschwentner et al, 1995a). In order to obtain a more precise 2.…”

Tubulotoxic Mechanisms of Ochratoxin A

“…The determination of those key targets will improve our understanding of mycotoxicosis substantially. Low dose Non competitive inhibition of the Blockade of plasma membrane anion organic anion transport system [7,9] channels and Cl -/HCO 3 -exchange Inhibition of the organic cation [22,28,32, 33] transport system [7] Alterations in cellular pH and ClCell proliferation and hypertrophy homeostasis and of transepithelial H + [10,30] and electrolyte transport [22][23][24]28, 29] Impaired protein reabsorption [2,31] Activation of extracellular signalregulated kinases (ERK 172) [29] Cell dedifferentiation [28,29] High dose Decreased cell viability [7,10,30] Decreased cell viability [6,22,29] Leaky plasma membrane [7,30] Leaky plasma membrane [6,29] Impaired DNA synthesis [7,30] Impaired DNA synthesis [25,29] Impaired protein synthesis [7,31] Impaired protein synthesis [25] Reduced cell growth [7,30] Reduced cell growth [29] Cell detachment and general decrease Cell detachment and general decrease in transport activity [7,21,30,31] in transport activity …”

“…enzymeregulating messengers) and thereby, leads to the disturbance of cellular signalling and regulatory events (e.g. carrier inhibition [7,28], MAPK activation [29]). Those changes in cellular signalling and/or regulation result in specific changes in cell function and/or phenotype, leading to changes in renal function and finally to the possible disturbance of the whole organism homeostasis.…”

Inhibition by P1075 and pinacidil of a calcium‐independent chloride conductance in conditionally‐immortal renal glomerular mesangial cells

“…Cells from this mouse proliferate at 33°C in the presence of y-interferon but cease cell division at 37°C in the absence of the y-interferon . There is no difference in the absolute magnitude of the chloride conductance between cells grown in the different conditions, although differences have been found with respect to the effects of the nephrotoxic mycotoxin ochratoxin A which inhibits anion conductances in the renal epithelial MDCK cell line (Gekle et al, 1993 The absence of a dose-dependent relationship for concentrations of up to 10-11 M P1075 and 10-7 M, pinacidil, together with the continued inhibition following drug removal, suggested that these drugs might be irreversible inhibitors of the chloride conductance. This was confirmed by the 16 h incubations with low concentrations of the drugs.…”