Modulation of ionic currents in smooth muscle balls of the rabbit intestine by intracellularly perfused ATP and cyclic AMP.
The effects of intracellularly perfused ATP and cyclic-AMP (c-AMP) on ionic currents recorded from fragmented smooth muscle cells (smooth muscle ball; SMB) were investigated, using the single electrode whole cell voltage clamp method. The Ca2+ current was distinguished from K+ currents, using pipette solution containing Cs+, TEA+ and 4 mM EGTA. ATP enhanced the Ca2+ current dose-dependently between 0.3 and 10 mM, and slightly slowed the slow component of the decay of the Ca2+ current, while the steady-state inactivation curve remained unaffected. Intracellular application of 5'-adenylyl-imidodiphosphate (AMP-PNP; 1 mM) inhibited the Ca2+ current by competition with ATP, but c-AMP (up to 300 microM) had no effect. With a high-K+ solution containing 0.3 mM EGTA and ATP in the pipette and physiological salt solution in the bath, a net inward current with transient (Ca2+ dependent) and delayed (Ca2+ independent) K+ outwart currents were evoked. Increased concentrations of ATP (above 1 mM) but not c-AMP (up to 100 microM) in the pipette enhanced the transient K+ outward current. Neither agent had any effect on the delayed outward current. When repetitive stimulations of intervals shorter than 5 s were applied, the amplitude of the transient outward current was markedly reduced, and 100 microM c-AMP partially prevented this attenuation. ATP may act on the Ca2+ channel either by phosphorylating the channel protein or by other ATP requiring mechanisms, independently from those induced by the action of c-AMP.(ABSTRACT TRUNCATED AT 250 WORDS)
D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000266:Adenylyl Imidodiphosphate / Q000494:pharmacology; D000818:Animals; D003994:Bucladesine / Q000494:pharmacology; D000242:Cyclic AMP / Q000494:pharmacology*; D004594:Electrophysiology; D007422:Intestines / Q000166:cytology; D007473:Ion Channels / Q000187:drug effects*; D008297:Male; D009130:Muscle, Smooth / Q000187:drug effects* / Q000502:physiology; D011817:Rabbits; D013806:Theophylline / Q000494:pharmacology
D007473:Ion Channels; D000266:Adenylyl Imidodiphosphate; D003994:Bucladesine; D000255:Adenosine Triphosphate; D013806:Theophylline; D000242:Cyclic AMP