Cellular mechanisms of hormone and drug interaction in ion transport in the nephron

1 . Renal tubular action of CS-045(troglitazone)：CS-045 has been developed for the treatment of insulin resistant diabetes mellitus. the mechanism ofaction is assumed to be sensitization of insulin receptor rather than stimulation of insulinrelease. To elucidate the mechanisms by which this agent causes edema as a side-effect，we examined direct action of CS-045 on the rabbit proximal straight tubule (PST) perfused in vitro.By measuring the electrophysiological parameters representing HCO . D23 . conductance in thebasolateral membrane and Na-3HC0 - 23 - D2 co-transporter activity as determined by changes inintracellular ph (phi),我们demonstrated that CS-045 directly stimulates Na-3HC0我们demonstrated that CS-045 directly stimulates Na-3HC0 D23 D2 co-transporter activity in the基本membrane in a dose-dependent manner，leading to an increase in Na reabsorption in the PST. This would, at least in part，be responsible for edema caused by CS-045.(2) Renal tubular function of receptor/transporter式因为mice:我们established clearance technique to examine renal function of PGE2-knockout mice. In miceanesthetized with pentobarbital, constant iv fusion was performed from tail vein. Urine volume，osmolality and Na were measured on samples collected from the bladder. PGE2 caused significantincrease in urine volume and Na excretion in he control micebut not in the PGE2-recptor knockout mice. We succeeded to perfuse isolated PST from the kidney ofP-glycoprotein (P-gp) knockout mice. From the decrement of intracellular rodamin fluorescencetransport activity of P-gp was estimated It was shown that P-gp is critical for drug excretion fromapical membrane of PST by acting through mechanisms linking with activation of PKC和P1-3kinase in the control mice, but that P-gp knockout mice lack this function。

(1) Renal tubular action of CS-045(troglitazone): CS-045 has been developed for the treatment of insulin resistant diabetes mellitus. The mechanism of action is assumed to be sensitization of insulin receptor rather than stimulation of insulin release. To elucidate the mechanisms by which this agent causes edema as a side-effect, we examined direct action of CS-045 on the rabbit proximal straight tubule (PST) perfused in vitro. By measuring the electrophysiological parameters representing HCOィイD23ィエD2-conductance in the basolateral membrane and Na-3HC0ィイD23ィエD2 co-transporter activity as determined by changes in intracellular pH(pHi), we demonstrated that CS-045 directly stimulates Na-3HC0ィイD23ィエD2 co-transporter activity in the basolateral membrane in a dose-dependent manner, leading to an increase in Na reabsorption in the PST. This would, at least in part, be responsible for edema caused by CS-045.(2) Renal tubular function of receptor/transporter knockout mice: We established clearance technique to examine renal function of PGE2-knockout mice. In mice anesthetized with pentobarbital, constant iv infusion was performed from tail vein. Urine volume, osmolality and Na were measured on samples collected from the bladder. PGE2 caused significant increase in urine volume and Na excretion in he control mice, but not in the PGE2-recptor knockout mice. We succeeded to perfuse isolated PST from the kidney of P-glycoprotein (P-gp) knockout mice. From the decrement of intracellular rodamin fluorescence, transport activity of P-gp was estimated It was shown that P-gp is critical for drug excretion from the apical membrane of PST by acting through mechanisms linking with activation of PKC and P1-3 kinase in the control mice, but that P-gp knockout mice lack this function.