Effect of luminal nucleotides on Cl- secretion and Na+ absorption in distal bronchi.
P2Y receptor agonists stimulate Cl- secretion across both normal and cystic fibrosis (CF) airway epithelia, and therefore have potential for use in the treatment of CF. Although CF pathology is manifest primarily in the distal airways, most studies of P2Y-receptor-mediated airway epithelial ion transport have used cells cultured from proximal regions. Here we report the results of studies of P2Y-receptor-mediated ion transport in distal bronchi isolated from porcine lungs, cannulated and perfused. A luminal microelectrode was used to record transepithelial potential difference (PD) and cable analysis was applied to determine resistance (Rt) and equivalent short-circuit current (I(SC)). Luminal UTP (100 micromol/l) transiently hyperpolarized PD (from -5.8+/-0.3 to -6.5+/-0.4 mV) and increased I(SC) (from 47+/-6 to 55+/-8 microA cm(-2)) before inhibiting PD to below the pre-UTP level (-5.0+/-0.4 mV). The decline was attenuated by pretreatment with amiloride, and additional treatment with bumetanide inhibited the initial hyperpolarization, suggesting that UTP stimulates Cl- secretion and inhibits Na+ absorption across distal bronchi. Luminal addition of P2Y1 [ADP, 2-methylthio-ATP (2MeSATP)] and P2Y6 (UDP) receptor agonists had no effect on ion transport. Pretreatment with thapsigargin (0.3 micromol/l) did not prevent the UTP-induced increase in PD and I(SC) but attenuated the secondary fall in PD. Pretreatment with BAPTA/AM (50 micromol/l), however, had no effect on the response to UTP. Additional studies of isolated bronchial epithelial cells using Fura-2 showed that UTP increases [Ca2+]in, and this increase is blocked by pretreatment with thapsigargin. These results suggest that in intact distal bronchi luminal UTP stimulates Cl- secretion by a Ca2+-independent mechanism and inhibits Na+ absorption by a Ca2+-dependent mechanism. Both effects are likely to favour increased hydration of the airway surface, and may therefore be beneficial in CF.
Inglis
S K
SK
Lung Membrane Transport Group, Tayside Institute of Child Health, University of Dundee, Ninewells Hospital and Medical School, UK. s.k.inglis@dundee.ac.uk
Collett
A
A
McAlroy
H L
HL
Wilson
S M
SM
Olver
R E
RE
D000042:Absorption; D000244:Adenosine Diphosphate / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D001980:Bronchi / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism; D002614:Chelating Agents / Q000494:pharmacology; D002712:Chlorides / Q000378:metabolism*; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D004553:Electric Conductivity; D008839:Microelectrodes; D009711:Nucleotides / Q000494:pharmacology*; D058910:Purinergic P2 Receptor Agonists; D018048:Receptors, Purinergic P2 / Q000187:drug effects / Q000502:physiology*; D058473:Receptors, Purinergic P2Y2; D012964:Sodium / Q000378:metabolism*; D013552:Swine; D019284:Thapsigargin / Q000494:pharmacology; D013873:Thionucleotides / Q000494:pharmacology; D014530:Uridine Diphosphate / Q000494:pharmacology; D014544:Uridine Triphosphate / Q000494:pharmacology
D002614:Chelating Agents; D002712:Chlorides; D009711:Nucleotides; D058910:Purinergic P2 Receptor Agonists; D018048:Receptors, Purinergic P2; D058473:Receptors, Purinergic P2Y2; D013873:Thionucleotides; C070379:1,2-bis(2-aminophenoxy)ethane N,N,N',N'-tetraacetic acid acetoxymethyl ester; D004533:Egtazic Acid; D014530:Uridine Diphosphate; D000244:Adenosine Diphosphate; D019284:Thapsigargin; D000255:Adenosine Triphosphate; D012964:Sodium; D002118:Calcium; D014544:Uridine Triphosphate; C008501:2-methylthio-ATP