Potent inhibition of the aortic smooth muscle maxi-K channel by clinical doses of ethanol

Mechanisms and clinical implications of renal drug excretion

The body defends itself against potentially harmful compounds like drugs, toxic compounds, and their metabolites by elimination, in which the kidney plays an important role. Renal clearance is used to determine renal elimination mechanisms of a drug, which is the result of glomerular filtration, active tubular secretion and reabsorption. The renal proximal tubule is the primary site of carrier-mediated transport from blood to urine. Renal secretory mechanisms exists for, anionic compounds and organic cations. Both systems comprises several transport proteins, and knowledge of the molecular identity of these transporters and their substrate specificity has increased considerably in the past decade. Due to overlapping specificities of the transport proteins, drug interactions at the level of tubular secretion is an event that may occur in clinical situation. This review describes the different processes that determine renal drug handling, the techniques that have been developed to attain more insight in the various aspects of drug excretion, the functional characteristics of the individual transport proteins, and finally the implications of drug interactions in a clinical perspective.

Intestinal bile acid transport: biology, physiology, and pathophysiology

Intestinal reabsorption of bile salts plays a crucial role in human health and disease. This process is primarily localized to the terminal ileum and is mediated by a 48-kd sodium-dependent bile acid cotransporter (SLC10A2 = ASBT). ASBT is also expressed in renal tubule cells, cholangiocytes, and the gallbladder. Exon skipping leads to a truncated version of ASBT, which sorts to the basolateral surface and mediates efflux of bile salts. Inherited mutation of ASBT leads to congenital diarrhea secondary to bile acid malabsorption. Partial inhibition of ASBT may be useful in the treatment of hypercholesterolemia and intrahepatic cholestasis. During normal development in the rat ileum, ASBT undergoes a biphasic pattern of expression with a prenatal onset, postnatal repression, and reinduction at the time of weaning. The bile acid responsiveness of the ASBT gene is not clear and may be dependent on both the experimental model used and the species being investigated. Future studies of the transcriptional and posttranscriptional regulation of the ASBT gene and analysis of ASBT knockout mice will provide further insight into the biology, physiology, and pathophysiology of intestinal bile acid transport.