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Differential expression of P2X‐purinoceptor subtypes in circular and longitudinal muscle of canine colon
Author(s) -
Lee H. K .,
Ro S .,
Keef K. D .,
Kim Y.h .,
Kim H. W .,
Horowitz B .,
Sanders K. M .
Publication year - 2005
Publication title -
neurogastroenterology and motility
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.489
H-Index - 105
eISSN - 1365-2982
pISSN - 1350-1925
DOI - 10.1111/j.1365-2982.2005.00670.x
Subject(s) - myocyte , purinergic receptor , receptor , adenosine triphosphate , biology , depolarization , patch clamp , extracellular , biophysics , membrane potential , excitatory postsynaptic potential , chemistry , microbiology and biotechnology , medicine , biochemistry
Adenosine triphosphate (ATP) mediates excitatory junction potentials through P2X receptors in many smooth muscles. However, relatively little is known about postjunctional intestinal P2X receptors. We examined the effect of exogenous ATP on circular and longitudinal myocytes of canine colon using the patch clamp technique at 32 °C. In both cell types, ATP induced inward currents ( I ATP ) at −70 mV in a concentration‐dependent manner. The potency profile of ATP analogues in circular myocytes was: ATP ≈ 2‐methylthio‐ATP > α , β ‐methylene ATP, and that in longitudinal myocytes was: α , β ‐methylene ATP ≈ ATP > 2‐methylthio‐ATP. Pretreatment of circular myocytes with α , β ‐methylene ATP inhibited the response to subsequent ATP, suggesting receptor desensitization. I – V relationships of I ATP were linear with inward rectification and E rev of −13 mV. I ATP at −70 mV was carried predominantly by Na + as determined by shifts in E rev when extracellular Na + was lowered. In RT‐PCR, circular myocytes expressed mRNAs encoding P2X2, 3 and 4, while longitudinal myocytes expressed mRNAs for P2X3 and 5. P2X7 was absent in both cells. Fragments of each subtype were cloned and sequenced. We failed to clone P2X1 and P2X6 genes. Overall, different P2X receptor subtypes are expressed in circular and longitudinal canine colonic myocytes. Their activation produces non‐selective cation currents that can depolarize and excite muscles of both layers.