Intracellular accumulation of mercury enhances P450 CYP1A1 expression and Cl − currents in cultured shark rectal gland cells

Abstract

The effects of acute and subchronic exposure to mercury on the Cl − current (I Cl) were investigated in cultured shark rectal gland (SRG) cells. The effects of intracellular accumulation of mercury on cytochrome P450 (P450) were also assessed. Bath perfusion of a cocktail solution containing forskolin, 1-isobutyl-3-methylxanthine, and 8-bromoadenosine monophosphate enhanced I Cl. Addition of 10 μM HgCl 2 significantly inhibited the cAMP-activated I Cl ( p < 0.05, n = 11). Intracellular dialysis with ATPγS did not prevent the inhibitory effect of mercury on I Cl. In contrast, incubation of SRG cells with 10 μM HgCl 2 for 48 hrs markedly increased I Cl ( p < 0.01, n = 12). Dephosphorylation of the channel by intracellular dialysis with phosphatase I and II abolished the mercury-incubated increase in I Cl. The P450-mediated metabolite of arachidonic acid, 11,12-epoxyeicosatrienoic acid (11,12-EET), significantly increased I Cl. However, application of 11,12-dihydroxyeicosatrienoic acid (11,12-DHT) did not alter I Cl. Mercury incubation for 48 hrs did not alter the protein expression of Cl − channels, but caused an induction of CYP1A1 in cultured SRG cells. In addition, co-incubation of SRG cells with mercury and the P450 inhibitor clotrimazole prevented the mercury-incubated increase in I Cl. Our results demonstrate that acute and subchronic application of mercury has opposing effects on I Cl in cultured SRG cells. The acute effect of mercury on I Cl may result from mercury blockade of Cl − channels. The subchronic effect of mercury on I Cl may be due to an induction of P450 CYP1A1 and its mediated metabolites, but not due to an over-expression of Cl − channels.