Ca2+-channel-dependent and -independent inhibition of exocytosis by extracellular ATP in voltage-clamped rat adrenal chromaffin cells.
Membrane currents and capacitance were measured to examine the effects of extracellular ATP on exocytosis in voltage-clamped rat adrenal chromaffin cells. ATP reversibly inhibited Ca2+ current (ICa) and exocytosis. The dependency of exocytosis on ICa evoked by 1-s depolarizations was determined. However, inhibition of exocytosis was 2.6 times larger than that estimated from the reduction of ICa, implying the existence of a Ca2+-channel-independent pathway. This inhibition did not rely on a further reduction of the intracellular Ca2+ concentration spike. ATP reduced the rate of exocytosis induced by clamping the intracellular Ca2+ concentration. Pertussis toxin blocked the inhibitory effects of ATP on ICa and exocytosis. Although RB-2, a P2Y antagonist, blocked the inhibitory effect of ATP on ICa, RB-2 itself produced large increase or decrease in membrane capacitance. Adenosine inhibited ICa via a pertussis-toxin-sensitive pathway but did not significantly inhibit exocytosis. Our data show that extracellular ATP inhibits exocytosis via inhibition of ICa by activation of a pertussis-toxin-sensitive G-protein linked to P2Y receptors. Furthermore, our data strongly suggest that ATP activates another pathway, which is also G-protein dependent and accounts for the majority of the inhibitory effect of ATP on exocytosis.
Lim
W
W
Department of Physiology and Biophysics, Seoul National University College of Medicine, 28 Yongon-dong, Chongno-gu, Seoul 110-799, Korea.
Kim
S J
SJ
Yan
H D
HD
Kim
J
J
D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000311:Adrenal Glands / Q000502:physiology*; D000818:Animals; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000502:physiology*; D002838:Chromaffin System / Q000502:physiology*; D005089:Exocytosis / Q000187:drug effects*; D005260:Female; D019204:GTP-Binding Proteins / Q000502:physiology; D008297:Male; D018408:Patch-Clamp Techniques; D037342:Pertussis Toxin; D051381:Rats; D017207:Rats, Sprague-Dawley; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D015220:Calcium Channels; D010566:Virulence Factors, Bordetella; D000255:Adenosine Triphosphate; D037342:Pertussis Toxin; D019204:GTP-Binding Proteins; D002118:Calcium