Suppression by calmodulin of glutamate-induced potassium current in identified snail neurons

Regulatory roles of Ca2+/calmodulin-dependent protein kinase II and protein phosphatase 2A on the quisqualic acid-induced K+-current response in identified neurons of Aplysia

In identified B6 neurons of Aplysia buccal ganglia under voltage-clamp, application of quisqualic acid (QA) induces a unique slow K(+)-current response independent of G-protein. The response was augmented by raising the temperature in a similar fashion to the Phe-Met-Arg-Phe-NH(2)-induced K(+)-current response mediated by Gi/o. The QA-induced K(+)-current response markedly increased during the perfusion with Ca(2+)-free solution or after the application of W-7, a calmodulin (CaM) inhibitor. It was also enhanced by intracellular application either of H-7, a serine/threonine protein kinase inhibitor, or of KN-93, a Ca(2+)/CaM-dependent kinase II (CaMKII) inhibitor. Furthermore, the QA-induced response was markedly augmented by pre-treatment with 2,3-butanedione monoxime, an inorganic phosphatase. Intracellular application of protein phosphatase 2A (PP2A) significantly augmented the QA-induced response although neither protein phosphatase 1 nor protein phosphatase 2B altered the response. Application of either okadaic acid or calyculin A, protein phosphatase inhibitors, only slightly depressed the QA-induced response. Surprisingly, W-7 had no augmenting effect on the QA-induced response when examined after the application of either okadaic acid or calyculin A. These results suggest that the K(+)-current response is reciprocally but sequentially regulated by PP2A and CaMKII, the response of which the former is facilitating and the latter is inhibiting.

Nervous control of ciliary beating by Cl-, Ca2+ and calmodulin inTritonia diomedea

In vertebrates, motile cilia line airways, oviducts and ventricles. Invertebrate cilia often control feeding, swimming and crawling, or gliding. Yet control and coordination of ciliary beating remains poorly understood. Evidence from the nudibranch mollusc, Tritonia diomedea, suggests that locomotory ciliated epithelial cells may be under direct electrical control. Here we report that depolarization of ciliated pedal epithelial (CPE)cells increases ciliary beating frequency (CBF), and elicits CBF increases similar to those caused by dopamine and the neuropeptide, TPep-NLS. Further,four CBF stimulants (zero external Cl-, depolarization, dopamine and TPep-NLS) depend on a common mode of action, viz. Ca2+influx, possibly through voltage-gated Ca2+ channels, and can be blocked by nifedipine. Ca2+ influx alone, however, does not provide all the internal Ca2+ necessary for CBF change. Ryanodine receptor(RyR) channel-gated internal stores are also necessary for CBF excitation. Caffeine can stimulate CBF and is sensitive to the presence of the RyR blocker dantrolene. Dantrolene also reduces CBF excitation induced by dopamine and TPep-NLS. Finally, W-7 and calmidazolium both block CBF excitation by caffeine and dopamine, and W-7 is effective at blocking TPep-NLS excitation. The effects of calmidazolium and W-7 suggest a role for Ca2+-calmodulin in regulating CBF, either directly or via Ca2+-calmodulin dependent kinases or phosphodiesterases. From these results we hypothesize dopamine and TPep-NLS induce depolarization-driven Ca2+ influx and Ca2+ release from internal stores that activates Ca2+-calmodulin, thereby increasing CBF.

NMDA glutamate receptor antagonists selectively affect the synaptic mechanisms of nociceptive sensitization in snails

Defensive behavior command neurons LP11 and RP11 were studied in semi-intact snail preparations to investigate the effects of N-methyl-D-aspartate (NMDA) receptor antagonists on the mechanisms of nociceptive sensitization. Application of sensitizing stimuli to the heads of control snails led to membrane depolarization and increased excitability, and also depressed the responses of neurons to tactile and chemical sensory stimuli in the short-term stage and facilitated responses in the long-term stage of sensitization. Development of sensitization in conditions of exposure to the NMDA receptor antagonists AP5 or MK-801 produced changes in the membrane potential and membrane excitability of command neurons similar to those seen in neurons of control sensitized snails. In addition, changes in the responses of command neurons to tactile stimulation of the head and foot and chemical stimulation of the foot in these conditions were also similar to those seen in neurons of control animals. Acquisition of sensitization during administration of NMDA receptor antagonists led to pronounced depression of responses to chemical test sensory stimulation of the snails' heads in both the short-term and long-term stages of sensitization. Thus. in sensitized snails. NMDA glutamate receptor antagonists selectively acted on the mechanisms of induction of plasticity the synaptic "inputs" of command neurons mediating excitation from chemical sensory stimuli from the animal's head.