Involvement of Na,K-pump in SEPYLRFamide-mediated reduction of cholinosensitivity in Helix neurons

Abstract

SEPYLRFamide acts as an inhibitory modulator of acetylcholine (ACh) receptors in Helix lucorum neurones. Ouabain, a specific inhibitor of Na,K-pump, (0.1 mM, bath application) decreased the ACh-induced inward current (ACh-current) and increased the leak current. Ouabain decreased the modulatory SEPYLRFamide effect on the ACh-current. There was a correlation between the effects of ouabain on the amplitude of the ACh-current and on the modulatory peptide effect. Ouabain and SEPYLRFamide inhibited the activity of Helix aspersa brain Na,K-ATPase. Activation of Na,K-pump by intracellular injection of 3 M Na acetate or 3 M NaCl reduced the modulatory peptide effect on the ACh-current. An inhibitor of Na/Ca-exchange, benzamil (25 muM, bath application), and an inhibitor of Ca(2+)-pump in the endoplasmic reticulum, thapsigargin (TG, applied intracellularly), both prevented the effect of ouabain on SEPYLRFamide-mediated modulatory effect. Another inhibitor of Ca(2+)-pump in the endoplasmic reticulum, cyclopiazonic acid (applied intracellularly), did not prevent the effect of ouabain on SEPYLRFamide-mediated modulatory effect. These results indicate that Na,K-pump is responsible for the SEPYLRFamide-mediated inhibition of ACh receptors in Helix neurons. Na/Ca-exchange and intracellular Ca(2+) released from internal pools containing TG-sensitive Ca(2+)-pump are involved in the Na,K-pump pathway for the SEPYLRFamide-mediated inhibition of ACh receptors.

Na+/K+-pump and neurotransmitter membrane receptors

“…Results indicated that Na + /K + -pump was responsible for the SEPYLRFamide-mediated inhibition of ACh receptors in Helix neurons. Na + /Ca 2+ -exchange and intracellular Ca 2+ released from internal pools containing TG-sensitive Ca 2+ -pump are involved in the Na + /K + -pump pathway for the SEPYLRFamide-mediated inhibition of ACh receptors (Pivovarov et al 2007). The evidence for these inhibitory events being linked is as follows: (1) ouabain decreased the modulatory SEPYLRFamide effect on the ACh current; (2) there was a correlation between the effects of ouabain on the amplitude of the ACh current and on the modulatory peptide effect; (3) ouabain and SEPYLRFamide inhibited the activity of H. aspersa brain Na + /K + -ATPase; (4) activation of Na + /K + -ATPase by intracellular injection of 3 M Na acetate or 3 M NaCl reduced the modulatory peptide effect on the ACh current.…”

“…These results indicate that Na + /K + -pump is responsible for the SEPYLRFamide-mediated inhibition of ACh receptors in Helix neurons. Na + /Ca 2+ exchange and intracellular Ca 2+ released from internal pools containing TG-sensitive Ca 2+ -pump are involved in the Na + /K + -pump pathway for the SEPYLRFamide-mediated inhibition of ACh receptors (Pivovarov et al 2007). These results are summarized in Fig.…”

“…3A diagram to summarize a putative intracellular mechanism for a peptide-mediated reduction of neuron sensitivity to a chemical transmitter, for example, acetylcholine. P-R, peptide receptor; G-prot, G-protein; cADPR, cyclic adenosine diphosphate-ribose; ATP, adenosine triphosphate; IP 3 , inositol-1,4,5-triphosphate; RY-R, ryanodine receptor; IP 3 -R, IP 3 receptor; ACh-R, acetylcholine receptor; activation/increase of intracellular level, white/blue/orange arrow; inhibition of intracellular level, black arrowModified from Pivovarov et al (2007) …”