Ionotropic and metabotropic activation of a neuronal chloride channel by serotonin and dopamine in the leech Hirudo medicinalis

Abstract

Cl− channels on the pressure‐sensitive (P) neuron in the leech are directly activated by synaptic release of serotonin (5‐HT) and are indirectly stimulated by the cAMP second messenger pathway, suggesting an unusual dual regulation of the channels. We have investigated the mode of action of 5‐HT and dopamine (DA) on a Cl− channel in adult P cells in culture by recording from cell‐attached patches. 5‐HT increased Cl− channel activity only when included in the recording pipette and not when applied in the bath. Pipette or, more effectively, bath application of DA led to an increase in Cl− channel activity. This effect was blocked by the potent and specific dopaminergic (DA1) receptor blocker, SCH‐23390. The stimulation by DA, but not by 5‐HT, was also blocked by the cAMP‐dependent protein kinase A (PKA) inhibitor Rp‐cAMP and was mimicked by the membrane‐permeant cAMP analogue dibutyryl cAMP (db‐cAMP). Our results show that 5‐HT directly gates a Cl− channel that is also activated by DA via the cAMP pathway. This study demonstrates that a ligand‐gated channel can be independently operated by another transmitter acting via a second messenger pathway.

Mechanisms contributing to the dopamine induction of crawl-like bursting in leech motoneurons

“…A +1nA current injection increased the firing frequency of CV only to 23.0±3.0Hz in DA compared with 41.2±3.8Hz in normal saline. These results are consistent with prior observations that DA exerts a generally inhibitory influence on leech neurons (Ali et al, 1998;Crisp and Mesce, 2004;Sargent, 1975), but helps to enhance their patterned activity.…”

“…Although previous evidence suggests the presence of a DA 1 -like receptor in the leech (Ali et al, 1998;Colombaioni and Brunelli, 1988;Salzet et al, 1998), the pharmacological properties of this receptor and other subtypes may be distinct from other species. The leech likely has a second class of DA receptors not positively coupled to cAMP.…”

“…To begin to identify these mechanisms, we sought to determine whether crawling-related activity was dependent on cAMP second-messenger signaling. This approach was taken as the leech central nervous system (CNS) is known to possess at least one DA 1 -like receptor, which has been shown to be positively coupled to adenylyl cyclase activity (Ali et al, 1998). This activity, in turn, increases the cytoplasmic concentration of cAMP, thus enhancing protein kinase A (PKA) activity and the serine/threonine phosphorylation of cellular proteins, including ion channels possibly involved in neuronal bursting.…”

Dopamine stimulates snail albumen gland glycoprotein secretion through the activation of a D1-like receptor

“…The activated catalytic subunits can then phosphorylate specific intracellular target proteins and mediate the appropriate physiological response. The PKA inhibitors Rp-cAMP and H-89 suppress PKA-mediated signalling in a number of invertebrates, including leeches (Ali et al, 1998), crustaceans (Locatelli et al, 2002), insects (Hazel et al, 2003) and molluscs (Malagoli et al, 2000). Our results demonstrate that dopamine-mediated secretion of HdAGP might be a PKAindependent process because inhibitors of both the regulatory (Rp-cAMP) and catalytic (H-89) subunits of PKA failed to inhibit protein secretion.…”

Dopamine modulation of Ca2+ dependent Cl- current regulates ciliary beat frequency controlling locomotion inTritonia diomedea

“…Because Ca 2+ increases I Cl(Ca) amplitude and because I Cl(Ca) is decreased in the presence of dopamine or TPep-NLS, we suggest that dopamine and TPep-NLS are acting directly to block or reduce I Cl(Ca) . Dopamine modulation of Cl -currents has been reported in a number of different animals and cell types, including leech neurons, where dopamine leads to an increase in Cl -channel activity (Ali et al, 1998), and in rod cells of salamander retina, where again dopamine leads to an increase in I Cl(Ca) and Cl -efflux (Thoreson et al, 2002). Dopamine and TPep-NLS also increase input resistance by selectively blocking I (Cl -)leak .…”