PGE2 hyperpolarizes gallbladder neurons and inhibits synaptic potentials in gallbladder ganglia

Gallbladder prostaglandin E2 (PGE2) levels are significantly elevated in pathophysiological conditions, resulting in changes in gallbladder motility or secretion that may involve actions of the prostanoid in intramural ganglia. This study was undertaken to examine the effects of PGE2 on neurons of the intramural ganglia of the guinea pig gallbladder. Application of PGE2 by microejection or superfusion elicited a complex triphasic change in the resting membrane potential (RMP). For example, application of PGE2 by microejection (100 microM) resulted in a brief hyperpolarization (mean duration 11.1 +/- 1.3 s), followed by a mid-phase repolarization toward or above RMP (mean duration 50.7 +/- 8.1 s), and finally a long-lasting hyperpolarization (mean duration 157.3 +/- 36.7 s). Associated with these PGE2-evoked alterations in RMP were changes in input resistance measured via injection of hyperpolarizing current pulses. An examination of the action potential afterhyperpolarization (AHP) during the PGE2-evoked response revealed an attenuation of both the amplitude and duration of the AHP. However, only a slight increase in excitability of gallbladder neurons in the presence of PGE2 was evident in response to depolarizing current pulses, and PGE2 did not cause the cells to fire spontaneous action potentials. Application of PGE2 reduced the amplitudes of both fast and slow excitatory synaptic potentials. These results suggest that increased prostaglandin production may decrease ganglionic output and therefore contribute to gallbladder stasis.