Caffeine-induced chloride current in dissociated rat hepatocytes

Current responses to caffeine in single hepatocytes dissociated from adult rat liver were investigated with the conventional whole cell patch-recording configuration. Caffeine produced a sustained inward current (I-caf) with increasing conductance at a holding potential of -40 mV. The reversal potential of I-caf was close to the Cl- equilibrium potential. I-caf was not affected by the internal perfusion of l(caf)-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA) or Cs+, whereas the Ca2+-activated K+ outward current elicited by A-23187 was inhibited by intracellular BAPTA or Cs+. A 1 mM 3-isobutyl-1-methylxanthine (IBMX) was about equipotent to 1 mM caffeine in inducing the current. I-caf was not modulated by the external application of N-(2-[methylamino]ethyl)-5-isoquinolinesulfonamide (H-8), a cyclic nucleotide-dependent protein kinase inhibitor, or intracellular perfusion with guanosine-5'-O-(2-thiodiphosphate) (GDP beta S) or guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S). It was concluded that caffeine induced an increase in membrane Cl- conductance without utilizing the rise of intracellular free Ca2+ or adenosine 3',5'-cyclic monophosphate (cAMP) and without mediating G protein, suggesting the possible existence of caffeine receptor-Cl- channel complexes on liver plasma membrane.