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The function of the multidrug resistance 1 (MDR1) protein as mediator of the activity of stress-induced chloride (Cl-) currents under hypotonic conditions has been studied. Regulatory volume decrease (RVD) in four pairs of isogenic cell lines and 36Cl efflux in two cell lines with or without hypotonic stress were measured to investigate the relationship between the amount of MDR1 protein present and the size of the Cl- currents. There were no significant differences in RVD and 36Cl efflux rate between parental and MDR cells. This indicates that expression of MDR1 does not confer additional Cl- conductance.

The multidrug resistance 1 (MDR1) protein has been implicated as a vital element in drug transport due to its pumplike properties. Studies have also suggested that MDR1 can function as or mediate the activity of a stress-induced chloride (Cl-) current under hypotonic conditions. Herein, a study on the effect of hypotonicity and inhibitors on rhodamine 123 exclusion showed that MDR1's functions in drug transport and in Cl- channel-associated activities are separate and mutually exclusive.

Analysis of whether vacuolar H+-ATPase or Na+ H+ exchanger modulate intracellular pH (pHi) in J774 murine macrophage-like cells using 2', 7'-bis(carboxyethyl)-5(6)-carboxyfluorescein marker reveals that the J774 cells modulate pHi through an amiloride-sensitive Na+ H+ exchanger and through factors that block vacuolar H+-ATPases. Na+ H+ exchange helps recover acid load. A p-chloromercuriphenylsulfonic acid-sensitive transporter and H+-ATPases play a role in resting pHi.

Reports on the effect of hypotonicity and inhibitors on rhodamine 123 expression by multidrug resistance protein 1 (MDR1), or p-glycoprotein. Construction and properties of MDR cell lines; Rhodamine uptake assay; Cell surface expression of MDR1.

Infection of J774.1 murine macrophages by influenza A virus (IAV) induces two major responses, production of host defense molecules and death by apoptosis. We investigated whether induction of two cytotoxic compounds, tumor necrosis factor-alpha (TNF-alpha) and nitric oxide (NO), directly caused IAV-induced apoptosis, and whether induction could be modulated by interferon-gamma (IFN-gamma) or the replication competence of the virus. Live IAV potently induced production of both TNF-alpha and NO, but UV inactivated virus was a poor inducer of both molecules. When cells were pre-treated with IFN-gamma, inactive IAV became as effective an inducer of NO, but not TNF-alpha, as live IAV. Amantadine, which antagonizes viral entry and replication, partly inhibited TNF-alpha and NO production in unprimed cells, but did not inhibit NO in IFN-gamma primed cells. IAV-induced cytotoxicity was not due to the induction of TNF-alpha or NO. Cells were insensitive to either TNF-alpha-containing supernatants or to recombinant TNF-alpha. Anti-TNF-alpha antibody did not protect cells from IAV-induced cell death, and anti-oxidants that inhibited TNF-alpha production also failed to increase cell survival. Inhibitors of NO production did not protect from IAV-induced cell death, either alone or in combination with superoxide dismutase (SOD). We conclude that, even though IAV was a potent inducer of TNF-alpha and NO in macrophages, IAV-induced apoptosis was not mediated directly by them. Importantly, viral replication was not required for the induction of TNF-alpha or NO, and the action of inactive IAV could be potentiated by IFN-gamma.