Studies in mice with a targeted deletion of the adenosine 1 receptors (A1AR) generated in our laboratory have shown that the homozygous A1AR knockout animals lack the vasoconstrictor response of glomerular afferent arterioles that is normally elicited by activation of the tubuloglomerular feedback response through the macula densa pathway. We have therefore used these mice to elucidate the consequences of inactivated TGF control on the regulation of GFR and salt excretion. We found that A1AR knockout mice have a reduced ability to maintain GFR in response to an acutely reduced blood pressure, have a reduced renal vasoconstrictor response to an elevation in plasma angiotensin II concentration, and are less able to increase GFR during an acute volume expansion. Studies in a macula densa-derived cell line suggest that most of the adenosine found in the cell culture medium is derived from extracellular degradation of ATP since inhibition of 5? nucleotidase caused a marked reduction in adenosine levels. We have therefore made a knockout construct to target 5? nucleotidase with the expectation that the effects of a deficiency in this ectoenzyme mimicks A1AR deficiency. These experiments are currently at the ES transfection state. We have studied the mechanisms of the vasoconstriction elicited by adenosine in isolated perfused afferent arterioles of the mouse. Adenosine caused a persistent vasoconstriction in these vessels that was blocked by pertussis toxin and by PLC inhibition. Furthermore, L-type calcium channel blockade largely eliminated the vasoconstriction. Taken together these observations suggest that adenosine causes vasoconstriction by activating PLC through the beta/gamma dimers of the Gi protein and that the vasoconstriction is maintained by Ca influx through L-type Ca channels. To assess the role of the glomerular hyperfiltration in diabetes-associated nephropathy was have begun a series of experiments in Akita mice, a mouse strain with non-obese insulin-dependent diabetes mellitus. At six months of age male Akita mice were found to have an about 40-50% higher GFR than wild type controls confirming that these animals are a useful model to study the pathogenesis of the renal phenotype resulting from diabetes.
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