P2Y Receptors Present in the Native and Isolated Rat Glomerulus

Abstract

Extracellular ATP can mobilize intracellular calcium in rat glomeruli by interacting with P2Y receptors. However, the identity of the receptor subtypes involved is not known. In the present study, we have used RT-PCR to identify mRNAs for specific P2Y receptor subtypes expressed in the rat glomerulus: mRNA for P2Y₁, P2Y₂, P2Y₄ and P2Y₆ receptors was detected. Functional expression of P2Y₁ and P2Y₂/P2Y₄, but not P2Y₆, receptors in intact glomeruli was confirmed by measuring the relative stimulation of the inositol phosphate pathway induced by selective agonists of a particular receptor subtype. Finally, we have used available polyclonal antibodies to confirm the expression of P2Y₁ and P2Y₂ in the glomerulus, in mesangial cells and glomerular epithelial cells (podocytes), respectively; but we could not demonstrate P2Y₄ or P2Y₆ receptor expression by this means. In a separate series of experiments, we have examined the possibility that intra-renal sympathetic nerve terminals are a source of extracellular ATP and that this would be supported, though not excluded, by supersensitivity to ATP following denervation. Nucleotide-induced stimulation of the inositol phosphate pathway was measured in both control rats and rats that had been sympathectomized by intraperitoneal injection of 6-hydroxydopamine. The response to norepinephrine was measured as a positive control. In the sympathectomized rats, the effect of norepinephrine was significantly enhanced, whereas ATP-induced inositol phosphate production was unaffected, being similar in both groups of animals.