External ATP-induced changes in [Ca2+]i and membrane currents in mammalian atrial myocytes.
Fura-2 fluorescent digital-imaging microscopy and whole cell patch-clamp recordings were used to study the effects of externally applied ATP on atrial myocytes isolated from rabbit and guinea pig hearts. Application of 100 microM ATP elicited a transient increase in intracellular calcium concentration ([Ca2+]i), which was not suppressed by theophylline, whereas adenosine and ADP failed to evoke the response. The Ca2+ transients were suppressed by the application of Co2+, Ni2+, or verapamil and by the removal of extracellular Ca2+, indicating that the inflow of external Ca2+ is necessary to evoke the response. The Ca2+ transient was suppressed also by ryanodine, suggesting that the mobilization of intracellular Ca2+ is another important factor. In the whole cell recordings, ATP induced a transient depolarization of the membrane potential due to the activation of a rapidly desensitizing inward current which persisted in the presence of Co2+, Ni2+, verapamil, or ryanodine. These results indicate that in mammalian atrial myocytes, ATP evoked transient increase in [Ca2+]i via P2-receptor, through the release of internally stored Ca2+ associated with the inflow of external Ca2+. This response seemed to be triggered mainly by the influx of Ca2+ through L-type Ca2+ channel activated by membrane depolarization, which was caused by the ATP-induced inward current.
Hirano
Y
Y
Department of Cardiovascular Diseases, Tokyo Medical and Dental University, Japan.
Abe
S
S
Sawanobori
T
T
Hiraoka
M
M
D000241:Adenosine / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology; D002478:Cells, Cultured; D003035:Cobalt / Q000494:pharmacology; D006168:Guinea Pigs; D006321:Heart / Q000187:drug effects / Q000502:physiology*; D006325:Heart Atria; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects; D009532:Nickel / Q000494:pharmacology; D013806:Theophylline / Q000494:pharmacology; D014700:Verapamil / Q000494:pharmacology
D003035:Cobalt; D009532:Nickel; D000255:Adenosine Triphosphate; D013806:Theophylline; D014700:Verapamil; D000241:Adenosine; D002118:Calcium