Modulation of N-type Ca2+ currents by A(1)-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 va riant of the patch-clamp technique. Adenosine inhibited high voltage-activa ted (HVA) Ca2+ currents in a concentration-dependent manner with an EC50 of 313 nM and a maximal inhibition of 36%, respectively. Inhibition of HVA Ca 2+ currents in adrenergic and cholinergic MPG neurons was similar. Adenosin e 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 A(1) and A(2a) receptors. Ca2+ current inhi bition by adenosine was mimicked by N-6-cyclopentyladenosine, an A(1)-selec tive agonist (EC50 = 63 nM) and prevented by 100 nM 8-cyclopentyl-1,3-dipro pylxanthine, an A(1)-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 attenua ted 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 curren t inhibition by a conditioning prepulse to +80 mV. Finally, 1 muM omega -co notoxin GVIA occluded adenosine-induced current inhibition. Taken together, we concluded that adenosine inhibits N-type Ca2+ currents by activation of A(1) receptors via a voltage-dependent and PTX-sensitive pathway in rat MP G neurons. Our data may explain how adenosine acts as an inhibitory modulat or of ganglionic and neuromuscular transmission in the pelvic plexus.