Vol. 299, Issue 2, 501-508, November 2001

Modulation of N-Type Ca²⁺ Currents by A₁-Adenosine Receptor Activation in Male Rat Pelvic Ganglion Neurons

Kyu-Sang Park, Seong-Woo Jeong, Seung-Kyu Cha, Boo-Soo Lee, In Deok Kong, Stephen R. Ikeda and Joong-Woo Lee

Department of Physiology and Institute of Basic Medical Science, Yonsei University Wonju College of Medicine, Wonju, Kangwon-Do, Korea (K.-S.P., S.-W.J., S.-K.C., I.D.K., J.-W.L.); Department of Emergency Medicine, Asan Kangnung Hospital, Kangnung, Kangwon-Do, Korea (B.-S.L.); and Laboratory of Molecular Physiology, Guthrie Research Institute, Sayre, Pennsylvania (S.R.I.)

Modulation of voltage-activated Ca²⁺ channels by adenosine was investigated in male rat major pelvic ganglion (MPG) neurons by using the whole-cell variant of the patch-clamp technique. Adenosine inhibited high voltage-activated (HVA) Ca²⁺ currents in a concentration-dependent manner with an EC₅₀ of 313 nM and a maximal inhibition of 36%, respectively. Inhibition of HVA Ca²⁺ currents in adrenergic and cholinergic MPG neurons was similar. Adenosine did not modulate T-type Ca²⁺ channels present in adrenergic MPG neurons. Reverse transcription-polymerase chain reaction analysis indicated that MPG neurons express mRNAs encoding A₁ and A_2a receptors. Ca²⁺ current inhibition by adenosine was mimicked by N⁶-cyclopentyladenosine, an A₁-selective agonist (EC₅₀ = 63 nM) and prevented by 100 nM 8-cyclopentyl-1,3-dipropylxanthine, an A₁-selective antagonist. Conversely, CGS 21680, an A_2a-selective agonist, displayed a relatively low potency (EC₅₀ = 2200 nM) for inhibiting Ca²⁺ currents. The action of adenosine was significantly attenuated by 2 mM guanosine-5'-thiodiphosphate or 500 ng/ml pertussis toxin. The voltage dependence of adenosine-induced current inhibition was evident by 1) a bell-shaped profile between the current inhibition and test potentials, 2) kinetic slowing in the presence of agonist, and 3) relief of the current inhibition by a conditioning prepulse to +80 mV. Finally, 1 µM -conotoxin GVIA occluded adenosine-induced current inhibition. Taken together, we concluded that adenosine inhibits N-type Ca²⁺ currents by activation of A₁ receptors via a voltage-dependent and PTX-sensitive pathway in rat MPG neurons. Our data may explain how adenosine acts as an inhibitory modulator of ganglionic and neuromuscular transmission in the pelvic plexus.