Effect of cAMP on porcine ciliary transepithelial short-circuit current, sodium transport, and chloride transport.
OBJECTIVE
To investigate the effects of 8-bromo-cAMP (cAMP) on porcine ciliary transepithelial short-circuit current (Isc) and transport of chloride (Cl-) and sodium (Na+).


METHODS
With Ussing-type chambers, cAMP-induced changes in Isc, electrical resistance (ER), and transepithelial 36Cl- and 22Na+ fluxes were measured. Drugs were applied to the nonpigmented epithelium (NPE) and/or pigmented epithelium (PE) side(s). The effect of IBMX (1, 5, or 10 microM; 3-isobutyl-1-methylxanthine) on Isc-increase induced by 8-bromo-cAMP on the PE side was also tested.


RESULTS
On the NPE side, a single concentration (10 microM, 100 microM, or 1 mM) of 8-bromo-cAMP induced a biphasic (transient peak followed by sustained plateau) Isc increase. On the PE side, 8-bromo-cAMP induced a similar but delayed biphasic Isc increase at 1 mM, a slight plateau-Isc increase at 100 microM, and no Isc increase at 10 microM. In the concentration-response curve, the cAMP-induced peak-Isc increase became significant at a concentration 10,000 times lower on the NPE than on the PE side. At 10 microM, the cumulative cAMP-induced Isc-increase reached its maximum on the NPE side, but was virtually nonexistent on the PE side. IBMX (a phosphodiesterase inhibitor) but not 8-CPT-6-Phe-cAMP (higher permeability than 8-bromo-cAMP) significantly increased the peak-Isc concentration-response curve induced by 8-bromo-cAMP (10 nM-1 mM) on the PE side. On the NPE but not the PE side, 10 microM 8-bromo-cAMP induced a significant but transient increase in net PE-to-NPE 36Cl- flux (1.03 +/- 0.18 microEq/min per square centimeter; P < 0.001). Neither ER nor transepithelial 22Na+ flux was changed after cAMP exposure.


CONCLUSIONS
In porcine ciliary processes, apparently on the NPE side, cAMP triggers a biphasic (transient peak followed by a sustained plateau) Isc increase. Only the peak-Isc increase involves an increase in net PE-to-NPE Cl- transport.
Ni
Ying
Y
Laboratory of Ocular Pharmacology and Physiology, University Eye Hospital Basel, Basel, Switzerland. juneye.ying.ni@gmail.com
Wu
Renyi
R
Xu
Wen
W
Maecke
Helmut
H
Flammer
Josef
J
Haefliger
Ivan O
IO
D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology*; D000818:Animals; D002712:Chlorides / Q000378:metabolism*; D002924:Ciliary Body / Q000187:drug effects* / Q000378:metabolism; D000242:Cyclic AMP / Q000031:analogs & derivatives / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004553:Electric Conductivity; D017097:Electric Impedance; D004848:Epithelium / Q000187:drug effects* / Q000378:metabolism; D017136:Ion Transport / Q000502:physiology*; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D010857:Pigment Epithelium of Eye / Q000187:drug effects* / Q000378:metabolism; D012964:Sodium / Q000378:metabolism*; D013552:Swine; D013873:Thionucleotides / Q000494:pharmacology
D002712:Chlorides; D010726:Phosphodiesterase Inhibitors; D013873:Thionucleotides; D015124:8-Bromo Cyclic Adenosine Monophosphate; C015929:8-((4-chlorophenyl)thio)cyclic-3',5'-AMP; D012964:Sodium; D000242:Cyclic AMP; D015056:1-Methyl-3-isobutylxanthine