Modulation of N-type Ca2+ currents by A1-adenosine receptor activation in male rat pelvic ganglion neurons.

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 A2a 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 A2a-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 microM omega-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.