Functional expression of three P2X(2) receptor splice variants from guineapig cochlea

Functional expression of three P2X(2) receptor splice variants from guinea pig cochlea. J. Neurophysiol. 83: 1502-1509, 2000. ATP has been suggested t o act as a neurotransmitter or a neuromodulator in the cochlea. The respons es to ATP in different cell types of the cochlea vary in terms of the rate of desensitization and magnitude, suggesting that there may be different su btypes of P2X receptors distributed in the cochlea. Recently three ionotrop ic P2X(2) receptor splice variants, P2X(2-1), P2X(2-2), and P2X(2-3), were isolated and sequenced from a guinea pig cochlear cDNA library. To test the hypothesis that these different splice variants could be expressed as func tional homomeric receptors, the three P2X(2) receptor variants were individ ually and transiently expressed in human embryonic kidney cells ( HEK293). The biophysical and pharmacological properties of these receptors were char acterized using the whole cell patch-clamp technique. Extracellular applica tion of ATP induced an inward current in HEK293 cells containing each of th e three splice variants in a dose-dependent manner indicating the expressio n of homomeric receptors. Current-voltage (I-V) relationships for the ATP-g ated current show that the three subtypes of the P2X(2) receptor had a simi lar reversal potential and an inward rectification index (I-50 (mV)/I_(50) (mV)). However, the ATP-induced currents in cells expressing P2X(2-1) and P 2X(2-2) variants were large and desensitized rapidly whereas the current in those cells expressing the P2X(2-3) variant was much smaller and desensiti zed slower. The order of potency to ATP agonists was 2-MeSATP > ATP > alpha ,beta-MeATP for all three expressed splice variants. The ATP receptor antag onists suramin and PPADS reduced the effects of ATP on all three variants. Results demonstrate that three P2X(2) splice variants from guinea pig cochl ea, P2X(2-1), P2X(2-2), and P2X(2-3), can individually form nonselective ca tion receptor channels when these subunits are expressed in HEK293 cells. T he distinct properties of these P2X(2) receptor splice variants may contrib ute to the differences in the response to ATP observed in native cochlear c ells.