Species differences in regulation of renal proximal tubule transport by certain molecules.

Renal proximal tubules (PTs) play important roles in the regulation of acid/base, plasma volume and blood pressure. Recent studies suggest that there are substantial species differences in the regulation of PT transport. For example, thiazolidinediones (TZDs) are widely used for the treatment of type 2 diabetes mellitus, but the use of TZDs is associated with fluid overload. In addition to the transcriptional enhancement of sodium transport in distal nephrons, TZDs rapidly stimulate PT sodium transport via a non-genomic mechanism depending on peroxisome proliferator activated receptor γ/Src/epidermal growth factor receptor (EGFR)/MEK/ERK. In mouse PTs, however, TZDs fail to stimulate PT transport probably due to constitutive activation of Src/EGFR/ERK pathway. This unique activation of Src/ERK may also affect the effect of high concentrations of insulin on mouse PT transport. On the other hand, the effect of angiotensin II (Ang II) on PT transport is known to be biphasic in rabbits, rats, and mice. However, Ang II induces a concentration-dependent, monophasic transport stimulation in human PTs. The contrasting responses to nitric oxide/guanosine 3',5'-cyclic monophosphate pathway may largely explain these different effects of Ang II on PT transport. In this review, we focus on the recent findings on the species differences in the regulation of PT transport, which may help understand the species-specific mechanisms underlying edema formation and/or hypertension occurrence.